I had a two channel M-1 with no options (no output tranny, no meters, purchased new directly from the John Hardy Company)
It's a very well-made unit. Fairly fast-sounding preamp based around the 990 op-amp, good attack, good hi's and low's. beautiful midrange, but can still let an aggressive source through without mellowing it out or making it sound sterile. Has a tightness to the sound that is somehwhat like an api, kinda sorta. (A friend of mine liked these so much, he replaced the opamps on the 2-buss of a fairly capable API desk with Hardy 990's and loved it.)
It was a very, very versatile unit for my work (fast hardcore/punk, random classical remotes, hip-hop, acoustic "rock"). Kick, Snare, overheads, toms, bass guitar, electric guitar, acoustic guitar, hammond...vocals. It never sounded bad on a source, IMO, generally sounding damn good. For stuff i generally went to an API on like kick, bass guitar, It usually slaughtered it sonically, though the color of an API may be what you or the track would desire. For stuff where a slower pre may be more appropriate, I usually prefered the Hardy as well.
Sonically, it is damn good. Seems true to the source, in a better than average way. My biggest problem was deciding if color or sonics were more important to the source. I usually just caught it with the Hardy, and colored it somewhere else if it needed it.
As for the options...
I've used m-1's with the VU option, and it's the best metering system I've ever used.
I've used m-1's with both transformer and no transformer, but I haven't directly compared them. I think I prefer no transformer, but it wasn't a drastic enough difference to make me hold to it. The transformer may be worth it just for the sake of interfacing with unbalanced sources, like the eq input of an earlier Amek or something. It's failry easy to swap out, and these options, as well as channels, can be added later piece by piece.
John Hardy is a hell of a nice guy as well.
Hopefully I'll be buying one again soon.
They could sell for double what they go for...