Thorn resistant tubes are just regular butyl tubes but have thicker walls. They're intended to prevent punctures because the offending pointy thing has to go through a thicker piece o' rubber. Slime tubes allow the puncture but then seal it with magical goo. I've heard the Slime tubes work pretty well for small punctures and not so well for bigger ones. Tire liners (the strips your shop is offering) prevent punctures by adding an extra layer of stuff for the offending pointy thing to go through but they're also another thing to deal with when changing a flat. None of these things will prevent flats entirely. Nothing will. And all of 'em will make for a little heavier and rougher riding wheel. I'd recommend a good belted tire (like Specialized Armadillos, Continental Gatorskins, Panaracer Tourguards, etc.) and being prepared for and getting proficient at changing flats. As always, just my $0.02.