We (wife and I) have been wearing them for years just because I thought it was a good idea, and agree with the many comments above, after a few rides you get completely comfortable wearing it and now its just part of riding gear, that adds a little warmth and when sized correctly, you can snug it up tight and helps support the ole back.
We had a little incident last year that really made me a believer and Tek-Vest advocate: The wife and I were up in the UP zipping up trail 3 north of Bruce Crossing where the trail at times is a road, and then wow, a logging truck pulled out in front of us, I got stopped about 5 foot from the truck (thanks to studs, I also huge believer in studs) but my wife didn't see it as quick as i did due to snow dust and ended up hitting the truck. The truck was basically at a 45 degree angle, she hit the truck in the fuel tank and she flopped up against the door, her sled and her ended up underneath the load of logs. Her sled was up against the drive axle and her rear bumper was wedged in behind the fuel tank. She was laying on the ground right underneath the drive shaft. we got WAY WAY LUCKY, she ended up having a sore right side Wrist, arm, shoulder and ankle. it could have/would have been so much worse without the Tek-Vest and studs.
Please stud your sleds and wear Tek-Vests, Accidents do happen. Ending note: Michigan is a no fault state..............
CW