Recently picked this up in a trade from this very forum (thanks Simon!) and feel compelled to sing it's praises - what a pedal!
Ran it through my Mesa Express 5.25+ last night and it just brought everything to life. The Mesa has a bewildering array of tone options with Bass, Mid and Treble knobs along with with 2 additional alternative EQ enhancements - a 5 band graphic and a contour dial.
Even with all these options, the Diamond just does something magical - even just using the clean boost side of the pedal. Switching in the tone stack on the Diamond and scooping out some mids resulted in a really sparkly clean tone which I couldn't replicate with the amp controls alone. Beautiful.
I know a lot of forumites really like the Xotic EP as an "always-on" tone enhancer and I can see the Diamond being used in a similar way - I didn't want to turn it off. Maybe it's just hitting the amps preamp with a bit more "uumph" that brings out the best but I'm really surprised at the effect a good clean boost can have on your sound.
I've been through a few "clean" boosts lately including TC Spark (full size and mini), Rothwell Atomic Booster, and VFE Rocket EQ boost (currently back with VFE as I'm convinced it has a fault) but the Diamond stands head and shoulders above them in terms of the effect it has on the tone i can get from my amp.
Mind you, I still want to get my hands on a Suhr Koko Reloaded for the sake of curiosity..........