No idea, but on Amazon, it says that the 'Boginabag' package comes with a stool. Blimey, quality control really does put modern goods through their paces!
I have a Highlander folding toilet that I got in sale a few years ago in preparation for when I start camping properly. Stable (mostly - just check it each night) and packs flat. I've only used it once and I used the wooden cat litter that everyone here raves about and am now officially a fan.
I also set up the luggable loo from go-outdoors for some little-'uns to use. It's a bucket type and so doesn't meet your initial request but if you have space then it's worth considering - it is more stable, larger, and has a lid not something you really consider about the folding ones - they are open-topped). Although it isn't a folding loo; it doesn't have internal fittings like a flushing toilet - so you can fit some of your kit in it when travelling and so it isn't a huge drain on boot space.
From memory the bog in a bag was one of those tiny tripod things - I didn't like the look of that at all!
The Highlander Portable toilet that "Craftsmad" mentioned works well genuine bags are available or you can use waster bin bags. Biggest thing with them is they pack flat and take up very little room. Highlander toilet
Yes another vote for the Highlander does what it says in the bag and folds flat
------------- Experience enables you to recognize a mistake when you make it again.
Everything has been said before, but since nobody ever listens we have to keep going back and saying it all over again and again and again