Pros....it starts up without hesitation. Idles where you set it via the wizard. Also can use the wizard to control timing if you also have hyperspark distributor.
Cons....I've had to replace the O2 sensor already. Also, some people have had issues with loose injector wiring (easy fix though) or bad Sniper units and had to have them replaced. I've had mine retuned on a chassis dyno when I had the transmission swapped and while it did unlock a little more HP, the tune that the shop gave me made the car "stumble" more until it was fully warmed up. To be honest, a good carburetor will probably be easier to dial in than a Sniper.