I remember like it was yesterday when I bought this modern blue helmet. I say modern because it has vents in the design to get air in while cycling.
I remember the positive feeling I got from going from an older style helmet (plain white and styrofoam in construction) to this.
One of the biggest boons for the Serfas brand, from browsing internet reviews of the brand, is its fit, and I can speak to this. I have been pleased with its snug fit and performance in keeping my head cool.
I also was happy for the price. This cost me only $30 at a local bike shop, and all things considered this is a good value compared to what else is in this price range.
Without any proof to bear, I also feel like this is a quite aerodynamic helmet. Put your head down and lower your body while going down a hill and you gainfully get more speed. (At least the impression of it.) Of course, this is a bit of a platitude as anytime you lower your size to the wind while going downhill you go faster on a bike, but the helmet's shape at least helps with this some.
The helmet also has a brim on it, but I haven't found this to greatly improve keeping the rain off of me when going through wet conditions.
For the price point, this has been a good helmet. I thankfully haven't had a crash while wearing it, so I cannot speak to its safety, but the Serfas Cosmos does meet CPSC standards, as all helmets are required.
For thirty bucks, this is an effective and stylish helmet. Great color too.