I believe you mean Nite-Ize. I converted two mini-mags (2xAA) with the complete kit (head + tailcap switch). The advantage of the tailcap switch is that it allows the light to be turned on and off more quickly, and to allow the light to be switched while using it tactical-style. One of my two converted lights was used at work, and since I used that light often, the faster switching was appreciated. Keep in mind though, that the light must be tunred on the normal way for the tailcap switch to work. What I would do was leave the light switched on the normal way while I had it out for use and switch it off the normal way when I put it away. If it isn't going to be for a light you use very often, though, the tailcap switch isn't going to offer any significant advantage.

The focus is not adjustable.

The pattern is flood.

I thought the overall output was decent, so the LED head is a worthwhile conversion - but don't pay a lot for it. I wouldn't pay more than around $10. The other major advantage is much longer battery life, and not having to worry about the bulb burning out.

I should mention, though, that the head on the light I used at work broke after I accidently slung the light out of my hand onto a cement floor. So I have to say that I have doubts that the LED heads are extremely rugged. Since the pouch I carry (a Pock-Its, also from Nite-Ize) was designed for a mini-Maglite, I looked on flashlightreviews.com for a replacement that would fit well. I decided on a Fenix L2P, which I am very satisfied with. Much better output than the converted Mini-Mags.

In summary, the LED head is worthwhile if you can find it cheap. I'd recommend the tailcap only if you use the light often. The LED-converted Mini-Mags are decent general-purpose lights and would be good for an inexpensive light for your vehicle (assuming you already EDC a light) or to have around the house or as a backup.