Update to last post: the tread is still on after being tacked and shows no sign of wearing off anytime soon!
I also went back again with two pairs of boots - one suede and one synthetic - to have treads put on in an effort to make it through another winter without killing myself on a tile floor.
As they examined them, they noted the heel on one was wearing down (and quickly - I only had that pair for a couple days) and said I should take it easy or else it would wear into the actual heel and they'd have to re-build it later on and it'd be expensive. I opted for them to re-do the entire heel then and there.
The heels looks GREAT and they use a high-quality rubber, securely tacked on. They gave me a half-tread on both boots and they're much better than one I got last winter from somewhere else.
Price: $24 for a 2x half-tread on each. $20 for 1x heel rubber ($68 total)
Time (for two pairs): 1 week
Compare to another cobbler last year where a half-tread was $40, twice the time, and has since begun to peel off and the "tread" is now slick.