I have one of these and like it a lot. It is built like a tank, so is pretty indestructable. (Weight is around 700g if this matters to you.)
The bag seems very waterproof, though a little condensation forms at the foot end. Newer more breathable membranes may stop this, mine is 2 or 3 years old now but still going strong.
The zip is a good size, though as with all bivi bags, getting in can be an effort, especially in the rain. I use a one-point basha (from Kathmandu trekking) to give extra shelter in poor weather.
The olive green is a fantastic colour for wild camping here in the UK.
There are ligher bags on the market, there are also more advanced ones with poles etc, but I find the discovery to be easy to use and robust.
If insects are to be a problem, then the Discovery may not be for you, the TN Jupiter (?) has a mesh door so that you can have a view/breeze without bugs getting in and eating you.
--
Mark.
