They eliminated punctures for me, but eventually the friction between the tire liner and the tube wore a hole in the tube and caused a flat. Some folks have mentioned feathering the ends of the liners, to prevent this, but I never tried it. When those tires wore out, I switched to puncture-proof and ditched the liners.

Edit: Mine were some no-name cheap things. I was previously getting 3 or 4 flats a year, typically from bottle glass and little metal bits along the MUP. But since switching to puncture-proof, my flats have been limited to me doing stupid things myself, like pulling the stem off a tube, trying to get the pump head off.