The IPS-33B is famous for having the original Whammy chip built inside it. However, this unit is actually a multi effects processor. It can do more than just your average whammy sound, and Edge + Vai showcased that. It features everything you'd need to connect it to your rig -- MIDI implementation, a nice footswitch and so on.
Digitech did a good job with this unit in terms of overall implementation. The unit is easy enough to program that you don't really need the manual. The stock presets are also pretty cool. One of the biggest complains I have is that there is some tone suckage with this unit. It's not that transparent, and if you have a serial loop, it'll show. The unit is dated, so it's kinda understandable, but if Rocktron were able to make transparent effects in the 80s, why couldn't Digitech? One feature I really liked was the ability to run an expression pedal straight from the back of this unit. You don't need a MIDI footswitch with an expression pedal output. It just makes life easier when programming certain whammy effects.
The sound of this is pretty good, but like I said above, there's some tone suckage. Once you get past that, the whammy features really shine. Don't forget that this unit can also do that famous "shimmer" sound. Be sure not to get this confused with the IPS33. They're not the same unit, and the IPS33 goes for considerably less on the used market. This unit is actually almost identical to the DHP55 that the Edge used for a bit.
If you're looking for an intelligent pitch shifter and are on a budget, I recommend checking this out. Despite its flaws regarding the bypass, it's one of the best pitch shifters out there in terms of quality per dollar ratio. It's easy to program to boot. If you're going to get this, I recommend running some sort of mixer with it so you're not destroying your original tone.