I can give you a couple of specific complaints, but they're specific to models:
Raleigh Twenty:
- "You call that folded?"
- 165mm cranks by default
Birdy BD-1
- Flat handlebars. Can't someone invent a North Road that folds in half?
- Not an IGH. Derailer system turns into a mess when folded.
- I don't mind the 18" wheels - they're a fair compromise to get good handling with smaller-than-20" wheels - but frame needs to be designed to take 18" tires that are larger than 1.75" - if only for emergencies (if you're lucky enough to find an LBS with 18" tires, what happens if they turn out to be 18x2.0 kiddie tires?)
- I want the frame to lock automatically when folded, not when I shove the seatpost down.
- Darn thing isn't designed to roll without aftermarket bits.
- Aftermarket bits are ridiculous in price.
- Feels a bit noodly - I'd sacrifice a bit of weight for a slightly stiffer frame.
- Achieving non-standard design by making really weird engineering choices, resulting in parts that look like pieces from a bicycle shaped object, but were actually built to quality bike specs.
- If you put one zinc plated bit of anything on it, you don't deserve to build a bike. For crying out loud, dockless bikes have all-stainless hardware. No quality bike should ever be caught dead without this.
-Kurt