Used tire liners for a while a long time ago, including one double century. Made the bike so slow, I'd rather get flats. Probably slower overall with the liners. At least with flats you get a 5-10 minute rest. If I flatted every 50 miles with ordinary fast road tires, I might have a different opinion, but it's more like once every 500 miles. Practice changing tubes at home until you can do it flawlessly with no tools in 5 minutes. It's kind of fun, really.
I wouldn't use them on a rider but I very well might on a commuter. I used them extensively on my commuting bike when I lived in a city where glass on the streets was a problem. It allows you to run a somewhat cheaper tire (not a bad thing when commuting) and not worry about flats. I never had a glass cut with tire liners. I'm not running them now for my commute but the streets are clean where I live now and I am using kevlar belted tires.