All of the 3 mechanized HQ units are pretty OP.
In 1v1 there is still little reason to go for them except maybe for a puma but in team games all of these 3 vehicles are pretty OP.
The Flak HT is ridiciluos in it's damage capability and is incredibly hard to kill when its supported by shreck volks, plus you can abuse its setup time. It has "minimum range" which means jack shit since any kind of infantry based AT from allies is never going to get near to it or kill it, and againts light vehicles it can just use attack ground
The puma is nigh unkillable due to its high speed, high acceralation, smoke at vet 0 and good health for a light vehicle.
I think everyone knows how ridiciluos the walking stuka in team games , no question about that