The X300 works off of a constant on/off toggle and for momentary on you apply forward pressure to the toggle. You can press either the left or the right toggle forward so it is truely ambi. I've always only used TLR's, M3s, and M6s on my pistols, but I have run the X300 on a rifle. The x300 was mounted in the 12 o'clock on a FF rail in front of the front sight. It was easy to find the toggle with my thumb with and without gloves on. The only issue that I had with it was if I was really driving the gun for rapid follow up shots or even running it in burst, the toggle would engage and the light would stay on until I flipped the toggle back down/up.
I know that this could be corrected through more training with the light, but since I was already used to running the M600 I just switched back to it. I just didn't feel like dealing with another system when one already worked for me.
I agree that the "no wires" idea is great. I currently run my M600 on a pressure switch that is attached to my vert grip. I am only doing that while I wait for my offset mount to get in, cause I will then just run the light with a tail cap and my thumb. Surefire used to offer a tail cap for their Executive series light that was momentary only (Z54) that works great for the M600 and M300.
The biggest thing is to buy what you want, find the best way to run it that fits your needs, and practice practice practice.
Maelstrom: Are you running any type of light on your duty weapon right now? I can tell you that the X300 is comletely different than any of the Insight or Streamlight lights. The X300 is a bullet proof light that will last for a long time, but just be prepared to spend some time getting used to the interface.