I have three different styles of helmets and I've tried the ST with all of them. It doesn't work well with the full face Arai as it tends to get stretched out as you are putting it on. I kind of expected this as other balaclava's, except the open face one I made, do the same thing. It is great though with my 3/4 Bell and my modular (flip up). There is give on the sides of those you don't have with the full face.
Pro's: Extremely well made, blocks the wind around my throat, and fits well. It does just what is advertised.
Con's: When I made my own I made sure the back section was really long. Your head is looking down to check guages and looking side to side to check lanes. This exposes the back of the neck to some of that 65mph wind chill, even with a good jacket collar. It may be just me being use to my custom made version, so this is not really a con, just a thought that two inches longer in the back would help.