I mostly like the suit and I suspect it does improve aerodynamics. I bought a size Small based on the fit information on the web site and it is quite snug but not uncomfortable when I'm on my TT bike. It feels a bit uncomfortable if I'm standing up walking around but I guess that's a common skin suit issue. They are supposed to be snug and they are not meant for standing up.
The material is light and comfortable in hot weather and the suit certainly looks like it should improve aerodynamics but I don't currently have a way to measure that.
As much as I like the suit I cannot give it 5 stars: (1) The zipper feels cheap and it sometimes binds a bit when trying to zip or unzip it. I have encountered this same problem with every piece of Castelli kit I have ever bought. I don't know why they want to put cheap zippers on expensive clothing. (2) The zipper does not go far enough down the torso to make "nature breaks" easy despite what the description says. I was surprised by that because my Velocissimo San Remo, also by Castelli, does have a (just barely) long enough zipper. (3) The fabric is VERY fragile. The first time I wore the suit I lightly brushed my shoulder against the large ring of my bike while putting the bike up on its storage rack and the fabric ripped. I put on some Tenacious Tape as an initial fix and I'll figure out a longer term solution at some point but I am quite concerned that the fabric will not hold up well when I have to pin on race numbers.
Update: I've worn the suit enough times to have gotten used to it. The fabric is holding up better than expected but it does NOT tolerate contact with rough surfaces. It is important to avoid getting the fabric snagged on things.
It's hard to be sure but I think this suit, even with its pockets, is at least as fast as my pocketless Pactimo skin suit.