I've been using them on all my hotends (even the older block ones despite they claim they don't fit), and I've not had an issue at all. Over time, the hole near the nozzle seems to get a little larger probably due to cleaning the nozzle off with a pair of needle nose pliers, but I've not have sort of blockage like you describe. All of mine are using the standard 0.4 nozzle, although for a while I had one with a 0.6 nozzle without an issue.