Allowing random lucky runs is fine. Normal incrementals are usually treated as specifically curated experiences, but they don't have to be, and they're usually more fun the more it feels like you're sequence breaking.
Incremental game players usually hate RNG in their games because it means you can't just brainlessly follow a guide, and allows you to blame bad RNG instead of your strategy. It's best to make sure you always have an RNG-less path to success in general anyway, though if it's possible to get extremely unlucky (e.g. getting 0 truffles if there's no alternatives) it'll be frustrating when it happens anyway.
In current balance, I'm pretty sure the haste potion is more important than the screaming mandrake for getting good runs, anyway. That one I'm curious about how you'll keep from being essential to get on every good run in the future, since it's kind of boring needing a specific RNG roll on that action (which has to be done pretty late in the run too, because of the no calmness gain side effect)