I’m using a generic PM3 Easy off Aliexpress I got years ago for like $20. Also have a “Proxmark3 X” from MTools, they both do pretty much the same thing. Placed FlexUG4 over the serial #, may or may not need a light bit of pressure but they both read it.
FlipperZero reads it fine (better with a MFGC), ChameleonUltra reads it okay also.