Works great. A bit tricky to get on with my HANS and helmet, but once in position it doesn't seem to obstruct either. My HANS sits at 20 degree incline and the collar has room in there without rubbing.
You put it in ice water or freezer for like 30 mins and you're good to go for a while.
Rich was a good friend and racing buddy from tlhe mid'80's. He and I talked about the CoolShirt many times when it was just an idea he had. Started out selling Medical Equipment. Was starting up the CoolShirt business at work and one day, they told him he was spending too much time with it and canned him. Got him serious about the CoolShirts.
One of the Best thing I ever bought. Block ice is better than cubes. (sandwich bags full of water and frozen before you leave for track works well). Found if I put balaclava in cooler and wrung it out before getting in car, worked even better. Nomex wasn't soggy, so it never dripped. A little baby powder in gloves helps, too.
I also kept a bottle or two of frozen water in the CoolShirt cooler. Handy if you get stuck out on course. Plus if your crew brings you a couple of extras to drink in impound, it adds a couple of pounds to your weight before you cross the scales....
Will admit, I'm a bit biased toward the CoolShirt stuff. A little CoolShirt trivia. Original names Rich kicked around were "Chill Factor" (I have one of those original units I still use. Seems there was a trademark issue with it and he had to change name), and then "Kool Shirt" (have one of those, too.). Both still work fine, if a bit worse for wear.
No real difference that I can tell. Newer stuff have better pumps, although mine has lasted since 2005. Tubing over the shoulders has given way due to HANS devices. Also choices like CoolMax, or Nomex over old plain cotton. Should fit well. Don't get too loose. You want tubing to be close to really cool.
You probably could but I'm not sure why you would. It would be too cold at the start and from talking with people "in the biz" being too cold is just as distracting as being too hot. You want to be at a comfortable temperature to be at your peak performance.
FWIW, IMO the MOMO shirt is better at distributing the heat transfer across your body. It uses a large cross section bladder for the water to flow through as opposed to relatively small diameter tubing. As far as the ice box and other associated parts are concerned, I think they are all pretty similar for a sprint race application. I have seen the MOMO box last longer than a CoolShirt box in endurance racing but they are pretty close, say 2-1/2hr vs. 3-1/2hr. That would have been 5 years ago though, CoolShirt may have updated their product since then. No matter what, if you are getting overheated in the car, ANY of them are better than nothing.
Just as Dave worked with the CoolShirt guy when it was first developed, I worked with the creators of the MOMO shirt. They originally were designing a system (which we did the testing for) that would electrically cool the water rather than using ice. It was intended for 24hr events where you didn't want to be changing out boxes during pit stops. They did eventually get the system working, but it ended up being so expensive only the really big Rolex teams were using them, so to increase market share they developed their own ice box to work with their shirt, they also intentionally designed their shirt to work with CoolShirt and F.A.S.T. systems since they knew people wouldn't want to buy a whole new system. Anyways, that's the useless trivia from my past
EDIT TO ADD: I believe the CoolShirt and F.A.S.T. systems use different connectors at the shirt, so if you want to use a CoolShirt with a F.A.S.T. system, you need to change the connector on the end of the tubing that comes out of the shirt. If you drive other people's cars at all, it's a good idea to have both style fitting with you just in case.