I have a Phrozen Sonic Mini printer, and of course I'm eventually going to need to replace the FEP film on the resin vat. Is there anything I need to take in to consideration when buying some replacement film? Will any legitimate FEP film I find on Amazon work?
Any FEP film you find will work fine with any SLA printer you come across. Some may work 'better' or 'worse' depending on the quality of the film, but, for the most part they will all just work.
The caveat is that you must ensure the film is of the correct dimension for the resin vat, If it's too small you may be unable to clamp the sheet in taut enough to get a proper seal.
ASWELL, Some SLA printers do not have a standard 'sheet' style FEP, instead opting for a proprietary/semi-proprietary 'cartridge' style FEP. In these cases, unless you can find some form of 'adapter' or aftermarket upgrade, you will be unable to swap FEP films outside of said cartridges sold by your printer manufacturer.
In the case of your Phrozen Sonic Mini, It looks like it uses the standard sheet-style method, You should have no problems with replacing the FEP with an aftermarket sheet.