I've got one and reckon its the equivalent of a two-season bag in terms of warmth, and needs modding/supplementing if you are planning a camp when it's a bit chilly. Pay particular note to ground insulation as I think it doesn't fair to well in that area. Most people use a foam mat in addition to their primary matress, and some also add a foil sheet blanket. I used a IKEA matress topper quilt on top and a self-inflating mattress tucked between the wool mix blanket and the outer, but found this then made space inside the bag quite constricted. Next time I'll use a thin foam mat as the bottom layer with the self-inflater on the outside. I may also invest in a wool blanket to use an additional upper layer.
These things are bulky. The 'compression' straps mean that you can fold them into a fat squarish shape which could conceivably fit inside a large pack but it wouldn't leave much room for anything else and most people just roll them up and carry them separately. I suppose they could be lashed to a pack but it could make the load quite unwieldy.
Incidently, don't bother buying the separate carry bag available for these. It's just a large drawstring bag with a simple carry handle. I think it actually makes the roll more difficult to lug about as it prevents access to the compression straps which can be used as a handle or a carry strap. I guess the bag is useful for storage or as additional rain protection but it's not a great piece of kit.
The roll I'd heavy and bulky certainly, but factor in price an it starts to make sense. Unless you can afford to buy a high-tech ultralite bag then I think it starts to compare reasonably well against the competition. I was in Cotswold Outdoor yesterday looking at Van go bags in the sub-£75 bracket but walked on because I felt that although they were a lighter , they weren't hugely less bulky and the small benefit didn't give much over the bedroll. Plus, the bedroll seems a little more flexible in terms of its expandability/mod ability, it looks good, and its very cheap. So despite it's drawbacks I think it's a good bit of kit.