The big difference for me is in how the OCSD works with drive pedals. Both the Tech21 VTDI and the Aguilar TH I have used in the past are fantastic DI's and preamps in their own rights, but I was never happy with how my drive pedals sounded direct. It didn't matter what I did. They always sounded "harsh", "fizzy," or "buzzy" (hard to describe, subjective terms, I know). With the OCSD I finally like how my overdrive and distortion pedals sound. It's not "night and day" different, but it's significantly better. Being able to tame the high end and dial up the low end, the mid punch you can get, and the "whump-whump" sensation you get from the resonance knob are fantastic. The resonance is really the "secret sauce" to me. It's the key to making it sound like a miked speaker, in my opinion. It makes a big difference if you're running direct and ampless. And the headphone amp is a huge bonus for practicing. You're going to hear exactly what you'd hear coming out of the DI, so it's easy to dial in the exact sound you want to send to the house.