Was a 'pricey' purchase for my home studio, but to my ears, it was well worth it. I previously owned the PreSonus BlueTube, and that's my reference point for the difference in audio.
Using an AT 4040, SM57/58/Beta, and comparing the two, I found the Summit to have a bit more... presence. It seemed to be a lot more sensitive to the Mic's output. I initially noticed this effect when I whispered into the mic. The Summit seemed to pick up all the tiny details. It was a lot more dimensional.
As for regular vocals, the Summit had a 'smoother' sound, while remaining crispy and detailed. The Presonus seemed a bit more 'tinny'. I wasn't aware of this 'tinny-ness' until I heard the difference between the two.
I also recorded acoustic guitar with both. They were both pretty good, though the summit seemed to bring out a bit more detail and body.
I also heard a huge difference when it came to recording Bass guitar. That really jumped out at me. The Summit had a lot more fullness in the lower frequencies, and didn't seem to go into clipping mode while still outputting good volume.
I'm someone that usually does my best to avoid buying into the (often expensive) hype, and look for the best bang for my buck. I gotta say, this was a worthwhile investment. I really was inspired by the better quality of this preamp, and feel like my recordings have gone up a notch.
It's also built like a tank, and you can peek inside and see the quality of the soldering and the components, as well as the knobs. It looks like it was hand built by a audio geek, as compared to my PreSonus, which feels like it was assembly line built by worker #49385 eager to get to his lunch break.
Peace