As for the weight, it IS heavy for by bivy standards. However, that doesn't matter if you're pleased!!!! Don't switch to something else (unless you like it better - no matter what someone else says.
That bivy is less breathable than most, but is very stormworthy. It has a big storm flap over the zipper, right?
I prefer my equinox bivy, but I have to use a tarp with it to stay dry.
I would have something over my head in the rain in addition to the bivy for a few reasons:
-I would be claustrophobic in that thing if not open
- it won't breathe very well
- your other gear will be drier w/ at least a small tarp
Enjoy it! Todd