iOS Compatible Bluetooth Receipt Printer

Can anyone recommend a BT receipt printer for iOS?

I googled this and checked on Amazon. The problem is that they all talk about their wonderful app, and I’m not sure if it’s required or just an easy way to print “right”.

I’m looking for something that I can print to just like it’s a tiny printer - which it is, but it needs to behave in the OS like that.

Any recommendations would be appreciated.