I have one of the miltary sleep systems, MSS. As others have said, very heavy and bulky. The Gore-Tex bivy cover is great, as long as it comes to you in servicable condition. The system is not something you are going to want to pack very far, too heavy.
I mostly use mine only for car camping. I di use the GT bivy on outings that I use a tarp instead of a tent though.

The price is good, but if you look around, I have seen them as low as $120, new in the packaging. That way you are sure of the condition.

One more thing, since this is a military item and there ae those that will buy anything military, that also means there are imitations out there. The genuine system is made by Tennier Industries.