iOS Bluetooth compatible Printer

My client use some portable bluetooth printers. Now he want to use it with iPad.

I want to know that : How can I check that any printer is compatible with iPad (iOS 7 or 8) bluetooth or not?

I get some question here :

Bluetooth printing from iPad?

Printing from an iPhone

iPad portable printer

But it all talk on some specific modal(s). I want to know minimum requirement of any printer to be connect with iPad printer. Client current printer is Bluetooth 2.0.

Let me know if you need more info. in comment.

Thanks to have time to read.