I used to use some cheap, beginner signature picks, but as soon as I started playing more heavy music, I found the need for a thicker, more sturdy pick, and I found that these worked perfectly. I've yet to break one, and they're difficult to lose, given their big size.
I bought these on a whim along with the Jazz III XL Reds to try them out, as they are not usually my pick of choice. When I tried them it became apparent that they do not wear as quickly as other delrin/tortex picks and they have a slightly clearer attack. They have good grip thanks to the imprinted logos and I find they have a smooth release over the strings, I usually use these now for playing bass but found them great for playing guitar too and they are fantastic for pinched harmonics on the guitar. My only problems with these picks is the way they are rated by dunlop as either "Red" or "Stiffo" with no particular size specified, however the Stiffo picks seem slightly thicker and heavier and produce a slightly more warm/overdriven/muddy sound when you dig into the strings which can sound attractive.
I have used the Jazz III XL for about 5 years and it is by far, my favorite plectrum. I use it for djent and metalcore, so it is quite comfortable, especially for patterns and sweeps. It is thick and durable(I actually still have a couple of 'em left from my first pack, so they do last long). There is no downside for me. They are just what I need. I prefer them over the regular Jazz III, because with these, I can really feel the playing.