I did an e-bike conversion kit on a regular bike with a Bafang 750w mid drive kit. I did so without any research on how these kits compare to out of the box e-bikes. Sounded like a fun project (it was) and I liked the idea of it coming as various components that could be replaced, if needed. That said, I do like it, and it can move this fat guy around.

Some upsides that might be of value to you is you get to choose how powerful the motor is and what size the battery is. You can use an ebike range calculator to determine what fits your needs. I used this one https://reallygoodebikes.com/pages/electric-bike-ebike-range-calculator

I would feel confident riding it in rain/snow. But I haven't yet put it to that test. I doubt the kit would work on a foldable bike. While it's certainly heavier than a stock bike, I still find mine easy to lift. I think I could lift it for a couple flights of stairs without it being much of a strain.

It does take time and effort to do. You have to remove your pedals, cranks, bottom bracket, brake levers, and possibly the chain as part of the installation. If that's not something you want to do then the kit isn't a good choice, of course.