I used to use these when I commuted on two wheels. Recently when I had a flat on my BA I remembered tire liners and installed one, along with a new tube, on my 29’er wheel. So far so good.
Now I’m thinking of putting a similar liner in my road tire wheel set.
Anyone else use tire liners and, if so, are they working for you?
I used to use them, but some of the thorns I encountered went right through. Now I use tire slime. Since I’ve put the slime in my MUni and 26er I haven’t gotten a single flat. There was a point where I had a slow leak in my 26er, but the slime seemed to patch it up.
So what’s with the ‘slime’…do you goop it into your tube or between tire and tube somehow…? 
The Slime goes inside the tube. You remove the valve core. Squirt the Slime inside the tube. Replace the valve core. Then pump up the tire normally.
I’ve never actually used it myself. I’ve also never used a tire liner. I don’t ride in areas that have thorns or other extreme puncture hazards so I’ve never felt the need for extra puncture protection.
The shop buzz was that Slime didn’t really work that well and ended up globbing up and debalancing your wheel.
A long while ago I was having flats on my road bike and bought a pair of Kevlar tread tires (700 x 23). A little heavy, and kindof expensive, but I haven’t had a flat since. Since I’m not racing, I never notice the weight, but I definitely notice not walking home in riding shoes.