I ran a 2 carbine class with a TLR-1 on a Magpul Rail Light mount. The day after the class I took it off and ordered a hand held light and mounted it in the Magpul mount. Unless you only ever plan on using the light indoors for home defense, I'd want something with a bit more throw. Trying to engage a target a 100 yards in the dark wasn't very easy with the TLR-1. Also, I found the switch on the TLR-1s, and I'm sure X300 would be the same, to be "clunky" to turn on and off while on my rifle. I turned it on by accident more than a few times during the class as well. I'm sure some use tape switches, but I'm not in that boat.
I agree with the instructor's view on tape switches. It tethers your hand to where the switch is preventing moving it if you need the light on but have to shoot from an unconventional stance or position. Also, that cord getting caught on something might totally disable if severed or damaged enough.
If you don't want to break the bank, check out light from a company called ThruNite. They're only available on Amazon, or their website. I just got their TN12 in today, and for $49.99 it's pretty damn impressive. 1050 lumens out of a 2 cell light. I have a Streamlight Pro TAC HL3 that's 1100 lumens but it takes 3 cells and even though I got it for a good deal it was almost twice as much. The ThruNite was very comparable to the beam on the Streamlight. Just the Streamlight's throw was a bit further. I'll probably get their TN11s to mount to a weapon to see how it works out and if it can withstand the recoil.