Not much of an effects guy, most of the time it's guitar>cable>amp, but I just picked up the new TC Electronic "Spark" booster, and I cannot say how much happier it's made me with the sound I am getting from ALL of my guitars and amps.
I have two Blackstars; the little one (HT-5R) is way too tinny, and the bigger one (HT Club 40) is a bit too bassy. I'd never used a clean boost before, but I actually ordered a second one I was so pleased - going to use them "always on."
In addition to the DB boost and gain (not using any gain) it has active bass & treble controls, and three selectable frequency ranges. With the bass cranked, the little 5 sounds absolutely gigantic, and with a moderate treble boost on the 40, the single coils of the Siggy and Mira just jump right out, like a blanket was taken off of the amp. Biggest difference is on the clean channels; on the dirty ones, with same settings, just a little extra grit, quite pleasing.
There is minimal additional noise, and I can actually use my chorus and delay without killing my tone.
Like I said, I'm not an effects guy (or a professional endorser) but I love this thing, and wish I had popped my "clean boost cherry" long ago!