In stead of trying to find the exact sized postage bags I now just buy over sized and carefully wrap the items up, it works out cheaper than having 5 or 6 different sizes, and a lot less bother too.
This batch of bags were opaque, would have liked them a little thicker, but I haven't had any trouble with them ripping and they seal well.
4/5 from me, would buy again from this seller.
For what its worth, my tip is to buy a roll of black shrinkwrap pallet wrap, 500mm wide is better, wrap your items up in the pallet wrap then finish of with a postage bag. If the postage bag does get ripped, or someone tries to take a peek the shrinkwrap acts as a great safeguard, that stuff takes some effort to tear open when its been wrapped around your parcel a few times.