The biggest difference between Vtech and Maha dynos in our area is that on Maha dyno, Szymon will try to imitate real road conditions as much as possible but both Vtech dynos in our area have closed room and no cooling fans.
I have been on Vtech dyno and MaHa dyno with my car and during dyno run, I noticed a big difference of car sound ect... If on MaHa dyno, all my runs ended with big bang and fire out from exhaust, on Vtech dyno - nothing like this.
Torque numbers where pretty similar on both dynos but regarding crank power values, there was a 10% difference.
Same thing with bone stock i30n from one of my local friends - factory power figures where measured out only on MaHa dyno.