I ordered the Lexicon MPX-1 along with a 128 channel MIDI interface, the ESI M8U. I didn't get a chance to hear the M-One XL version, only the older one. The other cheaper reverbs I sampled were the Lexicon MPX-100 and 550. The 550 sounds really good, but then I found this German online store that had a deal on the MPX-1, I just couldn't resist.
I just hope they approve my order. I had to send them copies of my Visa and photo-ID, talk about paranoid. Most people probably just give up at that point.
-tek