Bicycle double frame bag

I’ve bust my saddle bag. Which is a bit of an (under) arse (storage issue).
So, since I’m researching my buying options for its replacement, I thought I’d write a post to share my findings.
To be clear, I’ve not seen any of the following bags in the synthetic material flesh (or if I have,mountain bike rear pannier bag they’ve been in the background to other bike shop adventures). I’m not able to provide you with a hands on review.
Instead, this is something of a meta-analysis (a systematic review; a hedge fund of funds). In other words,bicycle backpacks I’m going to surf the internet, looking at saddle bags, choose and buy one and then report back.