I own both lights (MT21A and old E25 187 lumens)
Both are good lights.
Long time ago I made two reviews but are in Italian and I do not know if the translator is understandable.
MT21A:
http://goo.gl/KKV01z
old E25:
http://goo.gl/uoqEC8
I also made the photo and video comparison between the old E25 and MT21A.
Although Nitecore is more powerful (260 vs 187 lumens) the difference is small and hardly percebibile.
Be noted that the diffuser is available for the Nitecore MT21A in various colors, for Fenix not.
Regarding the Fenix E25 the old version is no longer in production (I hope the news is correct, I was informed by a seller)
Now it is on sale the new E25 260 lumens, it has light levels spaced differently and maximum power is only available clicking and holding the button (Burst)
I read many enthusiastic comments on this light, others do not.
However, it is a torch Fenix and I doubt it can give a disappointment
I recently bought the new Nitecore MT2A version 2015 (different led - 345 lumens) it throws a few meters in less but has a much wider beam, has become my favorite 2xAA.
Consider well the distance of use.
A photographic comparison of different types of LED (MT21A vs MT2A) you can find it here.
(at the bottom of the page)
http://www.candlepowerforums.com/vb/showthread.php?360784-Nitecore-MT2A-a-layman-s-review-Includes-pics-specifications-and-timelapse-video