Well, I’m using it in an iPhone 16 pro, but never bothered to figure out which lens it was using. Ithe widest lens I would use it on is a 38mm SA on 6x9 format as that is the widest that lens should cover…but I have Not tried it for critical composition on the camera at all - I’d go to either the ground glass or live view for critical stuff anyway, because I would be there to check focus and DoF anyway.
I do know that when set for a 47mm. (The widest the optical finder for the Handy will go) it’s pretty close to dead on for the FOV as shown by the handy optical finder for both 4x5 or 6x12 …,basically, it’s “good enough” for my simple needs.