I took along a few OPSaks on last season's backpacking trips. Overall, I was not very excited about their durability. Closing was always a finicky procedure. I didn't really have problems with tearing of their bigger bags, such as my food sack, but their little bags easily tore above the zipper lock, making using them after a chore. The big sack (I think it's 20x25) was about 1.3 ounces.
After some searching, I came across Basecamp Odor Barrier Bags. Apparently, they used to be known as NyloBarrier Bags, made by Lite Trail. Lite Trail still maintains a Facebook presence, and I see promotions there, but its web page seems to no longer exist. I now see these for sale on Amazon and eBay.
Reviews of the bags are positive. They are much lighter than an equivalent OPSak, something like .4 ounces for a size similar to the one I mention above. They use the equivalent of a twist-tie to close (in addition with a suggested twist procedure of the bag closure), and users seem satisfied with using this closure method. They seem to be competitively priced, or even less expensive than the OPSaks.
Has anyone had any experience in using these bags? Has anyone used these and the OPSak, and can give a recommendation of one versus the other?