@Jonatansofer, two things that I noticed was the difference in the battery capacity, 48V 13Ah for the DJ bikes and 48V 10.4Ah for the Addmotor bike. Less range with the latter. What was a little more concerning was the location of the battery behind the seat tube on the DJ Bikes. A lot of weight in the back with the motor also in the rear wheel. The Addmotor bike had its battery on the downtube (where a water bottle would normally go) and the motor in the rear wheel, so a better weight distribution.
Both are online products so access to service or warranty help is going to be up to you. Hopefully you have some bike shop reasonably nearby that works on ebikes that would be willing to help you. In the price range that you are considering there are a number of brand name quality ebikes, like Raleigh, etc., where service would be easier to obtain.
Those two bikes are two totally different designs & purposes, so only you will know what kind of riding you want to do or already do which will help you decide on the right ebike.
