the rad is like $300 more expensive at least and doesn't come with any help with assembly (should be pretty straightforward but there can be issues), or ongoing maintenance like the REI one.

But the rad also has like at least double the power of the REI, a much larger battery, and a throttle (could be a positive or negative depending on your preference), plus that beefy built in cargo rack. It also has bigger tires (3.3" wide instead of 1.95) which can be good for comfort and some terrain types, but means higher rolling resistance, harder to fit in certain types of bike rack, etc. (for example some common wall mounted bike racks where you hook the front tire and hang the bike by it won't take over 2.25", same with the buses in my area). The rad runner also has smaller wheels and may stand out more as it looks less like a regular bike. It all depends what you want, really. Rad is a more established name in ebikes specifically but the REI one is a lot closer to a regular bike (would likely be a lot more usable if the electronics died and you wanted to keep using it in the mean time before repairs, etc) and it comes with that REI maintenance.