I had an NDI (sold it), and I currently have the D10, EX10 and the Extreme.
I'm not at all impressed with the Extreme because it's basically an NDI with CR123 (and a lot bigger in diameter as well so it's a bigger lump in the pocket).
The EX10, in fact, is brighter than the Extreme on High, and the UI of the EX10 is more capable and easier to use intuitively.
The D10 is great for those who want to stay with the AA battery, and it's just as capable as the EX10 (as bright) when you use the 14500 rechargeable. While not quite as bright with an Alkaline or Lithium primary, it's almost unnoticeably so.
I must not have been paying attention because I have no issues at all with the "switches" (they don't have switches as such) on the D10 or EX10, and I don't recall even reading about a problem with them other than user confusion. I'll look for that.
In the end, if I had to have just one Nitecore, it would be the EX10 first, or the D10 if I just "had" to run with AA's.
The EX10 is barely larger in diameter than the D10 and is much shorter, and I'd even "dare" to compare the $50 EX10 to some of the custom lights that cost hundreds more (I'll allow them to remain nameless).
I'd buy half a dozen EX10's anyday before I'd fork over that much money for any of the "custom" jobs.
As far as the Extreme goes, I'll play with it for a while, but I think it's going to find itself to be a gift to someone I know this Christmas.
Knowing what I know now, I wouldn't have even bought the Extreme.
My .02