In all honesty, I'm directed people who ask towards Tigerlight these days. I don't like to think of it in terms of whether the M4 is "worth" more. There's no non-rechargeable out there quite like the M4 or M6, and there's no doubt that they are very high quality lights. But I can get the performance I want from a Tigerlight, provided I'm willing to deal with the heavier weight and the fact that it's a rechargeable (I think staying on top of rechargeable batteries is a pain). And using the TL feels "free", since it's rechargeable.
I'd be looking at the M4 if I felt the light was only going to be used infrequently, so that 1. battery costs aren't an issue, and 2. it is critical that I always have a feel for the charge state of the batteries.
I imagine if you want a more M4ish beam from the TL, you can use some write-right.
Joe