I don’t have any personal use of this but this item says it takes usb input and converts it to the connection that would come out of the printer from what I understand.  It may work, it may not.  There are no reviews that are helpful of the product.
I’m a software engineering intern at Square and have been working on Bluetooth printer support for iPad. This feature was released in our latest Square Register build and brings physical receipt printing using Star printers to a mobile customer base. Before this version, Register for iPad supported printed receipts through Star printers connected by WiFi and USB. Adding support for a new type of printer was a great choice for an intern project as it was a combination of building off of an existing hardware integration layer and extending it to support new concurrency requirements. Integrating this new feature into Square’s codebase was a great lesson of how a well-designed code base can make writing new code easier.
But my point is that an adding machine paper-receipt looks unprofessional in some businesses.  An inexpensive ink jet or better, a multitasking network office printer that is already in use would make a LOT more sense for me.  I’m sure they are robust and work fine, they just don’t suit my business and I don’t like being so limited in the TYPE of printer I can use.
I have a friend who runs a small shop and knew the Esky ES-CD01 Heavy Duty RJ-12 Key-Lock Cash Drawer would be perfect for his application. This drawer was a massive upgrade to the system he had been using. He had tried other drawers with different connections and designs, however this one was really the best.
This printer is fast. Thermal printers print very fast, and the internals are actually much simpler than the ones at my work. You simply open it up, drop the paper inside (yes, it’s a drop in, which makes it much easier to replace the roll once it has run out) and then feed the paper over the top.
If you are using your iPad or iPhone by itself with the Square app, you will not be able to use a USB Star Micronics Printer. You will need either a Bluetooth Receipt Printer, or Ethernet Receipt Printer. A good reason for going with Ethernet, is that you can have multiple devices print to one printer. If you are using an Android device, you can use either an Ethernet Receipt Printer, or and of the USB Receipt Printer stated above as long as you use the USB OTG(on the go) adapter. Please note, Bluetooth is not currently supported on Android for Square. 
Star Micronics TSP100Receipt Printer is the first All-in-One receipt printer on the market today!. The advantage of TSP143LAN Receipt Printer is evident for applications such as retail, restaurants, and convenience stores. TSP143LAN Receipt Printer is provided with all standard operating system drivers (Windows, Linux and Mac) and specialty drivers such as OPOS and JPOS. The printer is also directly supported in Square Register. Star has also included a number of embedded simple utilities that will enhance Retail or Hospitality CRM in POS applications and therefore make the entire experience simple. These printers come complete with every thing you need including printer, power supply, Ethernet cable, wall bracket and a roll of thermal paper.
Square Point of Sale on an iPad is compatible with a wide variety of third-party hardware accessories. Below, you’ll find a list of supported accessories, where to purchase them, and information on getting set up.
Bluetooth desktop receipt printer. Star printer, TSP654IIBi2-24, is the Bluetooth printer model which is one model in the TSP650 series of printers. TSP650 (654II), thermal, auto-cutter, Bluetooth iOS…
Make sure not to send your customers’ receipts to yourself. You’ll receive a payment confirmation after every successful transaction, and you can view payment details from your online Square Dashboard.
Star Micronics TSP100GT Fast, reliable thermal printing is a snap with the Star Micronics TSP100GT. This printer offers additional configuraiton, including embedded graphics and logos, adding flair to retail receipts. The TSP100GT supports iPhones as well, giving you an option for receipt printing with your mobile POS installation.
If you have a Square Stand, in addition to the printers above, you can use certain USB interface receipt printers. The following receipt printers are only compatible with the Square Stand, not the Square card reader:
@SSmobile @Kevin7 – I went ahead and moved both of your comments over to the thread where we are tracking this feature request. I totally understand your frustration and desire for Epson support. They make a mean printer that is also a fraction of the cost of most Star printers. I have personally passed this feedback along to our product team, and expanding compatibility is something that is top of mind for them. I’ll update this thread if/when this functionality is added in the future! 
POSGuys.com is here to help you find the right printer for your specific business needs. Call 800.903.6571 for assistance or email sales@POSGuys.com. If you’ve already purchased one of the Square Compatible printers from us and need help with your setup, email support@POSGuys.com.
Buy Used and Save: Buy a Used “Star Micronics Monochrome Receipt Printer” and save 74% off the $690.00 list price. Buy with confidence as the condition of this item and its timely delivery are guaranteed under the “Amazon A-to-z Guarantee”. See all Used offers.
58mm POS Printer 384 line Thermal Dot Receipt 12v USB Printer Set w/ Roll Paper Package Content: 1 x Thermal Printer 1 x Instruction Manual 1 x Printer Driver 1 x USB Cable 1 x Power Cord 1 x 58mm The…
It is a simple process all I can think is that square gets a percentage of royalties from their supported printer sales and thats why they are locking everything down to these ridiculously overpriced pieces of equipment. 
For future reference, the price is $149.95: store.lantronix.com/product_p/xps1001ne-01.htm (It’s not listed on the page that is linked to, so it took me a while to get what you guys were talking about.) – Mathias Bynens Mar 23 ’12 at 17:21
I started off the implementation of Bluetooth printer support by using the same concurrency model used by our WiFi printer code and running Bluetooth printing and printer discovery blocks on a global concurrent queue. I quickly found what appeared to be a non-deterministic bug — sometimes I could print a receipt with no problem, and other times it would fail part way through. What I was in fact encountering was a timer firing and searching for connected printers while the app was in the middle of sending data to a printer. While this behavior was perfectly acceptable in communication for WiFi printers (TCP supports multiple simultaneous connections), it totally broke down in the new communication channel. It became clear that some kind of mutual exclusion was necessary to prevent this kind of collision.
Overall, this is a great printer. I can’t complain about the price because for similar thermal printers, this is relatively cheap. Any cheaper and there are issues with printing mechanics and whatnot.

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