Looking For Rowing Machine Advice

[Robelus]

Hey guys,I'm looking at a couple rowing machines at Costco.http://www.costco.ca/Browse/Product....111&topnav=Any chance someone here has used either of these or can comment on the effectiveness of rowers in general?I've tried running on a treadmill in the past but the jarring on my knees resulted in a lot of pain and I had to quit. I'm looking for something that is compact and I can store away in the spare room when I'm not using it but can still give me a good calorie burn. I've looked at ellipticals as well but most of them are big and seem like they'd be hard to move around, so I'm hoping that a rowing machine might fit the bill for me.I've just never used one and looking for some general comments on them, at least from costco I can return it if it doesn't work out.Thanks guys,K