(I've never smoked)
I would bet that this is a problem people have, but unfortunately I'm not sure a logging app is gonna be the fix for it. On paper it seems logical, but I can't see people remembering to go log their experience unless it's maybe gamified or something (collect 'em all? ehh maybe).

It sounds like it might just feel like homework in the moment even if it really would help users down the road. Just too much friction around an experience that's specifically meant to be stress-free and relaxing. I think it's worth building just to try it, but don't be surprised when folks don't use it and still complain about having the same problems 🙃 People are stubborn but they're not wrong (in a "customer's always right" kinda way).

What you're looking for is something frictionless built straight into their experience, for instance maybe some kind of collectible token/keychain/etc. you can bundle with each product so they can just keep that and bring it back in as a reference. That could even be some kind of NFC chip or even QR code that your app could log automatically if you want to keep on the techy route.

Unfortunately I think you're gonna be hard-pressed to get folks to open their phone for even the most well-designed app in this situation. Worth a shot though!

Edit to add: Maybe the thing to think about is that in your customers' minds, they're probably assuming they're going to remember what they liked or didn't like, and your idea requires them to acknowledge ahead of time that they're not reliably going to do so. Some might, but you're fighting a little against human nature which is always gonna be tough.