Here is my opinion on the gauges I have.
Tachometer - I don't think I ever looked at the tach while racing. You don't really have time for it most of the time anyway. The recall feature doesn't do much good if you start the race in a lower gear and then shift up. A total waste of my money (imho). You aren't going to blow it up by over-revving it. That is what the rev-limiter is for.
Oil pressure - didn't work most of the time - another total waste of my money. There is a free oil level light installed on the dash. Just keep that in mind, and realize it will come on once in a while while you are racing so don't freak out about that.
Oil temp - I like having this one, but am I going to pull in because of a high reading? Pretty much not a chance in hell. Absolutely not necessary, but it is nice to have to satisfy my own curiosity.
Gear indicator - a nice gadget to have and was reliable. It was nice to look at the dash and make sure you were in the right gear on a start, but it really isn't too hard to figure that out without spending $225.
If I was to buy a new car now, probably the only gauge I might buy would be the gear indicator. I'll pass on the advice that I didn't listen to : Unless you are loaded with cash, don't waste your money on gauges. Spend it on the stuff that will really matter to you on the track. After having some experience on the track, I realize I should have listened to someone wiser than me.
Brian B #58