I've now received and had to return two of these go-karts (purchased from another supplier).
The first had issues with the chain wheel running out of true (sided to side) and poor concentricity, this lead to the chain scraping on the inside of the chain guard and chain tension moving from super tight to super loose in a crank revolution. This first kart also had a badly damaged decal. You could try searching a popular video sharing site for "Berg Buddy Issues" if interested in seeing (and hearing!) all these issues.
The second kart arrived and after checking for the issues found on the first kart (not repeated) I unfortunately found that the steering headset bearings appear to be full of a gritty contaminant - more of this could be heard inside the front end tubing and some could be tipped out of the steerer tube (obviously a different assembly to a bicycle). This contamination has resulted a stiff, noisy and non-smooth steering. The BFR hub also felt stiffer on this kart than the first.
Overall this go-kart has the raw ingredients for a fun and durable toy, it's just a shame that apparent manufacturing / quality control issues have twice taken away this potential.