The P20iX is a tacticool type 21700 size light. It's very floody - perfect for inside buildings or close range outside where you need a big field of view, and bright enough at 4000 lumens .
The bumps on the front are something super tough for breaking car windows etc - so I guess aimed at first responder types. I quite like the double clicky tail switch. One is a really solid on/off click and the other cycles between light levels.
It has two modes, I use it in the everyday mode where it remembers the light brightness from when you turned it off. There also a hard core mode where it always turns on in max.
The hard plastic holster has a hole in the bottom, which I assume is to avoid melting it with the 4 x 4 x CREE XP-L2V6 leds, but I have occasionally just turned it on in the holster for general lighting if I needed both hands.
Since it's quite easy to pull it out of the holster, I do have a slight worry that it will come out by itself if I'm clambering around somewhere - but it never has yet. The holster is intended for clipping on those massive duty belts - it would swing around a bit otherwise. I have a vague recollection it came with some clips to use on narrower belts but perhaps I've thrown them away.
The 21700 battery it needs is a weird Nitecore one with positive and negative contacts each end. I wasn't wild about that, but in practice I never carry spare batteries, so they can be weird or built in and it's no particular problem. If you really hate this idea, there is an optional caddy for 2 x cr123s - but less brightness and lower run times.
I was interpreting your comment as "I have lights that directly compete with the P20iX and the P20iX is better", but that's not what you meant.
Things have changed a lot since 2010, and a number of those changes are reflected in the P20iX:
Ah, sorry for the confusion. The point I was trying to make, is that the reason custom, or even built in, batteries don't bother me as much as they used to, is that I fully expect technology to produce better emitters (probably LEP) and battery technologies. So the benefit of having standard batteries to extend the lifetimes of my flashlights past ten years is reduced.