I can comment on the Blitz having owned one previously (i've gone back to stock solenoid/nistune remap/r32 actuator now).
As you say, with the DSBC, it goes on %duty cycle. The DSBC has 4 settings, not including off. There's an overboost feature, and a retard boost feature. It's a dual solenoid, so goes up to around 2.5bar so it's highly recommended for twin turbo big boost applications. The downside is that the dual solenoid is huge so it's a little hard to keep hidden in your engine bay. The only reason why the blitz would be noisier would be because boost is built earlier.
There's also the price difference. The DSBC Spec R is a lot more expensive than the Profec.
But, I was looking at TypeVu's Profec install today, and one thing I do like about it is that it's really easy to keep it all stealth especially with the neat solenoid unit.