Some of Sennheiser's products aren't the best, others are almost universally thought to be fantastic. It is a bad idea to rule out a manufacturer simply based on reports from people in forums who almost certainly don't know what they're talking about. Imagine if you saw someone advising against ATi because they had a Rage 128 and it sucked, or maybe because they put their video card in backwards and it broke.
That aside, the Icemat Siberia looks like it's a pair of headphones with a separate clip-on mic. There's nothing wrong with this approach, but if you don't mind using a clip-on mic then you would be better off avoiding it, and if you DO mind using a clip-on mic then you shouldn't even be looking at it. Either way, I'd say it's ruled out.