The testing they do for the registration is not even close to being a proper check of the worthiness of the vehicle so would advice getting it checked by a garage before purchasing. Most garages will do a thorough check for about AED 300 and it takes about 1 hour.
Tasjeel is easy but can take some time depending on what time you go in the day.
Good luck!
We bought a second hand car a few months back. Yes, process is easy although time consuming, so leave a few hrs. You do need your insurance first. Whether the testing is comprehensive, depends how busy they are I think. Maybe someone has more info but thought I'd at least let u know to get yr iinsurance sorted this morn.