I've got 4 HWLabs rads (SR1 240 & GTS-Lite 240 bought 3 years back and 280GTS & 280GTX bought this year) and despite thorough cleaning including Mayhems Blitz Part 1 there was very little that flushed out so in my experience their reputation holds.
Well I had three systems built for other users this year and all three have been terrible, so maybe its a quality control issue?