I just missed out on buying used MD250H for $6k last month!
I think both bikes are heads above Ninja 250 for race bike, being purposely designed as race-bike from beginning. Meaning frame is not overbuilt and super-heavy meant for 2 people. Bike design starts with frame and there's absolutely nothing you can do once that design is carved in stone.
From lookings specs, MD250H would certainly be faster machine. But how much would depend on rider.
head-angle 24.5 on MD250H vs. 25.5 on Tianda
wheelbase = 48.4" vs. 52.0"
weight 198-lbs vs 216
power 34.5hp vs 27.5hp
Every tiny little bit adds up to fractions of second on every corner and straight. I don't have concrete numbers, but differences in those specs I suspect would result in 3-5s faster laptimes on most tracks favouring MD250H.
For non-pro racing, that's not whole lot and rider-skill ends up making larger differences than that. For example, guy that finished ahead of me in my 1st AFM race was faster than me by 10s/lap. Now I'm 7s/lap faster than him, both on stock Ninja 250s with same mods allowed by rules.
I think for price, that TDR300 is great value! Best deal on track bike anywhere really. Maybe upgrade it to Ninja 300 engine or Banshee 350.