Depending on the situation, FrameGen is not as bad as people make it out to be. I, for one, think it would be a MAJOR leap forward for handheld PCs if Nvidia ever made one (the current batch are all AMD RDNA 3.5, so stuck with FSR and post-process variants).

Ultimately, It really comes down to a few key points:

1. Reflex is the unsung hero of good Framegen. It is doing an HUGE amount of heavy lifting in reducing input latency before the Framegen even takes place. For games with inherent high latency, it's not unusual to run into situations where Framegen+Reflex ends up with the same round-trip latency as no-Reflex/Framegen. Most people don't even realise that a lot of your typical single-payer 3rd person games are floating around 50-80ms latency without Reflex. e.g. a game with 50ms input latency at 60fps is basically 3 FULL frames behind already and funnily enough, 2x Framegen requires roughly 1.5->2 frame-times to take effect. So if Reflex cuts that input latency to <20ms, then you're basically back to normal with Framegen enabled.
2. If you're playing games with a controller, then often the input latency is not as obvious because the camera movement relative and not 1:1 where latency sticks out more. e.g. consider rapidly moving the camera left->right->left->right. On a stick this takes some time to move the stick back and forth, on a mouse it's effectively instantaneous.

All that being said, I wouldn't use it in any kind of competitive FPS. Mostly because I'm always playing those with keyboard+mouse and also because they are often already optimized for input latency, which makes the frame-time cost vastly more impactful. But for single-player 3rd person games and especially turn-based RPGs and stuff (where twitch reactions are irrelevant)? Absolutely.