While I am the proud owner of TC Electronic's D-TWO delay box, I was never a fan of the M-One. That has changed with the release of the XL. The new XL version of the M-One is a noticable improvement to the box, and simply sounds better than the original, to my ears anyway.
The first thing I noticed was that TC doubled the preset memory to 200. They also did a lot of programming, and included many more live-oriented patches. I found the presets to sound really quite good, even in the noisy NAMM environment. The slight metallic taste of the reverb tails that I objected to in the original M-One seem to have been fixed in the XL. Altogether I feel the reverbs sound smoother now.
Front panel editing has the typically well thought out TC design, making it a pleasure to tweak the sounds. However, the M-One XL still has a fairly limited number of editable parameters, like the M-One. This is not the box for tweak-heads! The parameters are well chosen, and for the most part will serve probably 95% of the potential users quite well. By way of comparison, the TC M2000 has MANY more parameters to play with, giving the user far more control over the end result.
The M-One XL looks like a winner, and not just for live use: it will work nicely in the studio as well. I think anyone who likes the original M-One will appreciate the improvements made in the XL version.
For more in-depth information: M-One XL PDF brochure (1mb)TC Electronic products at audioMIDI