my experience with my Leopard:
so my mr3680 died, and I got the 4074-2000.
the rotor has kind of an plastik coating, or glue, supposed to protect the kevlar/carbon-fibre
Measurements of the rotor is 49mm, the magnets about 41mm, and has little axial clearance, don't know if I keep it like that or not.
on the back, there's a little space, but I think that's ok:
overall quality looks good so far. didn't get hot on 5s, great.
good power, but different to the losi xcelorin 1700kv and the mr 3680-1600. Those have more torque at low revs.
good buy so far!