I'm a diehard Castelli fan. Their jackets,jerseys,and bibs always fit me like a glove. This piece does exactly what it's designed for, cool to cold temperatures with a base layer and you're good to go. For the record, I'm 5'6 and 150 lbs. Medium is perfect for me.
I love these booties. I wear them out every winter, lots of gross wet muddy Portland Oregon miles take their toll, but it's worth buying a fresh pair every fall. They are pretty darned waterproof (let's face it, nothing's actually 100% waterproof). They're also very easy to put on, the velcro closure on the back makes life easy.
So many shoe covers are really just designed for cold. But in Portland, rain is a much bigger issue. Neoprene covers get water logged and super heavy when wetmaking an uncomfortable situation worse! But these lightweight shoe covers are waterproof (at least from the top) and stay light even when wet. I use them with summer socks (Rapha Pro) and my feet dont get cold even when its in the low 30s because they are also very wind resistant. The Velcro attachment at the rear may not be as sleek as a zipper, but they are very easy to get on and off while remaining snug and sleek like a road shoe ought to be. The only thing that would make them better would be a reinforced toe and some tasteful reflection on the back and sides. Other than that, no complaints.
These booties are sleek, form-fitting, and aerodynamic. The double Velcro rear closure makes them easy to put on and take off. They are warm, and do a good job keeping the wind out. Keeping water out is a different story. They work well in a light rain or when the roads are wet, but they are definitely not waterproof. They will soak through in less than an hour in a heavy rain. In addition, they seem a little delicate - the bottom of one is already fraying around the cleat opening (I use Shimano SPD road cleats), and I've only had them for a few months.
I was looking for a more aero and form-fitting alternative to my bulky but definitely waterproof Gore Tex booties. These work well on damp roads or in a light rain, but when it's really coming down - which it often is in Portland - I'm sticking with the Gore Tex clunkers. They may be bulky, but they are more effective in really wet conditions. Plus, they are more durable. I'll go with the sleeker Pearl Izumis in milder conditions.