They are really nice slings. Since you already have a leather one, I'm assuming you know how it works for the most part. Some people have been turned off by it because it looked a little complicated.
I have used the Turner AWS several times in the Navy with the M14. It has a good grip and it holds well in wet conditions. I haven't had a problem with my sling stretching, but never used the leather one to really compare. I have been successful in chasing off rust on the ring and hooks, I do wipe it down a little bit after use. The rain, snow, dust, sand and other slightly annoying conditions haven't really affected the sling. It feels good when brand new, and gets better as time goes by.
They are fairly durable and I imagine does not need as much care as leather, a rag...fresh water and a dry place for storage. I'm not sure exactly what you're looking for, but for the most part I think you'll be happy with it. I will safely guess that if you like your leather sling, you'll probably like this one as well.