You can use the M20 with the stock OP relfector or have an accessoire SMO reflector for better throw. That already makes a difference, but I'll recommend to stay with the OP if you wanr a more or less universal light.
If you need a real thrower, there are better options, like the Jetbeam Raptor RRT-2 or even RRT-1 if size doesn't matter.
The TK11-R2 is a real tank of light, I still got mine, while I sold the M20 when I got the Titanium (basically the same as M21). It is much more simple, head loosen for Low (60 Lumen isn't low though) and head tightened for High. You may use it as a hammer if needed. I never compared it to the M20 in terms of throw, I guess it is more or less equal. If you want it simple and rugged, it's your light.
The M20 is more universal and has another UI, the T20C2 looks like its twin brother and probably behaves so, but the UI is different with a big chance of strobing instead of 3 times momentary IIRC...