I've heard some not-so-good things about those. The more powerful ones are a little better from what I hear. A lot of people may argue with me on this, but I think a good investment for you would be a decent set of pc speakers (one of the 2.1 systems with the powered sub.) They work quite well for mixing demos and jams. From you're other post I take it you're not looking to put out polished tracks or anything. In addition to a decent enough monitoring system, you will get a good set of speakers for your pc.
Some people have trouble getting the subwoofer to the right level with these speakers. The way I suggest getting around that problem is to hook them up to my computer and listen to a bunch of music I'm familiar with. Get the sub adjusted so it sounds right to you, and leave it set that way when you mix. When you get something that sounds good to you again, you've got a good mix. Hi-fi production it's not, but it works for me.
[edit] as others suggested, a decent set of headphones will help find any strange audio anomalies. again, something moderate and consumer oriented will do here. I can tell you're not looking for professional studio recordings, so why waste money on professional studio equipment?