I think they're well regarded. Speer are a pioneer and innovator.
They will have the following fundamental problems, though:
- loft compression will give you a cold back
- You will be bent like a banana
That's why I invented the 'Bridge Bag". There is a simple Nylon sheet supported by vertical cord stay under a 3mm Spectra line cable. It converts a regular sleeping bag into a warm, lie-flat hanging bed. It would also work with a bivi bag. You have to make small reinforced holes in the bag, but it won't affect the utility as a hammock or as a sleeping bag and if you can't find two suitable trees, you can still sleep on the ground.
You can read a detailed description, design, and review at hammockforums.net
http://www.hammockforums.net/forum/showthread.php?t=2059
It's in the public domain and royalty free to make or sell as long as I am acknowledged on the product and as a DIY project, it's extremely cheap and only an afternoon & evening's job.