Here's my feeling so far. I decided to go with a complete set from Cada and bought it from gearbest.
My buying experience with Gearbest was a mix between good and not as good as expected.
Firstly, I got my set (Cada C51041) for a little less than 40 euros and the price dropped by 6 dollars the day after. I wouldn't have been upset but the set was clearly not in stock and it took between 10-15 days before shipping. That being said, consumer service was great and offered to refund my GB wallet with 6 dollars and add extra points also. When I finally received my item I was quite happy. Tracking is good, no custom fees and you get the full item with original box and packaging.
Then, I tried to charge the battery box and it didn't work. I tried successfully to open it without any problem (no gluing so I just had to force a little to get the box opened). Soldering is not perfect but acceptable. I asked again the customer service and they tried to help. Meanwhile I understand that the included cable is mandatory to charge and that a standard telephone cable don't work. After charging the battery box work and all ports are available and tested at 8,4v.
I then checked the other parts to see if everything was good and found a broken shock absorber.
I notified the customer service that battery box was finally ok and the broken part but didn't expected they could solve that (in fact I didn't care) and they finally offered to refund the full amount or to set another set for free. So I'm currently waiting for a second set with battery box.
I'm overall happy with my purchase even if battery life seems pretty poor. It may be due to the fact that I choose to build the set with a gear ratio for speed and not for torque. It doesn't have great speed notheless but for sure there's quite no torque. I will build the second one with torque setting to compare. This set is currently at 32,59 € from gearbest (from phone app) and I think it's the best offer to get the battery box. Design of the crawler is not a copy from a Lego set and there's some slight change in the mold from most parts. Rims and tyres are really decent. L motor and servo are good even if return to center is not always perfect. There's some custom parts that don't exist in Lego. Red panels looks pretty poor in my opinion but at least they are not stealing Lego or moc design. There's an upcoming C51043 buggy which looks cool and will add PF lights. If you want to see more details from the opened battery box, you could search for Cada C51041.