alt Hacker NewsI really like a low speed throttle, like 3-5mph max is fine. 20mph is too fast and results in ebikes basically designed a motorcycles that cannot be pedaled. The throttle is so nice to have to get started quickly like turning left at a light, if you didn't have time to downshift before stopping, on a hill, or if the bike is heavily loaded with stuff. Its also nice to be able to use to slowly move between cars with your feet off the pedals to keep balance if needed.
Those are legal, at least in the EU. It's called "push support" or "walk assist", my bike engages it when I long-press the down button. It's purpose is to help you push the heavy e-bike up ramps and hills, but I mainly use it as a throttle when I ride behind my toddler on his balance bike.
It's closer to 3mph than 5mph, and as such needs some slow-riding skills, but it works.