Pros: Performance and flow rate (just like any of the other Mk20/25 first stages)
Cons: The material. Price, of course.
If it's any indication of how necessary the "ultralight" version of this regulator is, Scubapro stopped making it. True, it's lighter than a standard brass first stage, but not by much. Simply consider is a bad marketing ploy by Scubapro.
Being a Scubapro service technician, I see these Mk20 version come in frequently with significant pitting in the outer body. Also, the alloy appears to be much more brittle than the standard chrome plated brass - considering I've seen a few in the shop with rather large chunks taken out of them. This is something I've never seen with a brass first stage.
Their most notorious problem is in the aluminum alloy interacting with brass hose fittings and freezing the hoses onto the first stage. Scubapro implemented a fix by installing plastic bushings between the hose fitting and the first stage body. It helps some, but there's still contact in the threads. Unless the hoses are occasionally loosened and retightened, the hoses may never come off.
This regulator is of the same design as any of the other Mk20/Mk25 first stages. I would recommend any of the others over this one. If you're into the latest here-look-at-me technology, Scubapro now has a Titanium first stage. It's more durable and doesn't have problems with galvanic action....