I am happy with these bits. They did what I needed at a good price. I had to drill holes in acrylic sheet. Drilling on wood cracked acrylic. I read online that masonry pieces would work and bought them. Hakkin's masonry worked like a charm. Using a drill press would have been better, but the results I got with a hand drill were good enough. I used water and a fairly slow drill speed to keep the material cool. Can't speak for longevity and longevity because I use them very lightly.