Yeah they're different hole sizes, t100 have smaller holes, 500s won't work for the PL50S :)
And I've had 3 sets of the PL50S and they've all been great. Lost one set, broke the 2nd after a couple of years of them living in my pocket and going through the wash and the 3rd are still going strong.
I'm a Muppet... Apparently the isolation could be 100 or 500...
Pick the isolation one.
http://www.complyfoam.com/frequently-asked-questions/