Thanks all for your replies - apologies; I read them and then never replied.
I have a bike with a rack and some panniers for more serious loads, this is to be a bag for the "I''m off out for a ride" bike. I think the SQR system looks best for me given the lack of loops on my saddle, and so now it's a question of which size bag - do I want room for a stove and coffee-making stuff as well as the camera, waterproofs etc just because sitting in the countryside having a a brew is nice, or do I want the smallest one I can get away for 90% of the time for neatness?
Or do I just accept that I'm going to end up with more than one at some point? :-)
I've had my Carradice Pendle for a measly 6 years. A newborn by Carradice standards.
In that time, it's survived rainstorms, snow blizzards, a dunk in a river, numerous crashes, my fiancees cats, my dog and even being licked by actual real cows. And a horse! I've drilled holes in the bottom to fit a stiffener bar which I later removed and is still waterproof.
I went for the Pendle as it's an in-between size of the Barley and Nelson which seem more popular.
Here's the thing, prior to the Pendle, I like you used the panniers which as you know are just too big for most things. I also have a Carradice Maxi saddle pack and a smaller Topeak saddle pack. Every time I've used those packs I've regretted it. They leak and the space they offer is crap. We live (most of us) in a spot on the earth which is prone to sudden weather changes and for that reason, I keep a raincoat, spare tights, gloves, hat, and face covering in the bag at all times. I've lost count of the number of times I've dug that stuff out on what started as a pleasant day out. It works the other way round too. Getting warm on your ride? No probs, take a layer off and put it in your Carradice instead of tying it round your waist because that stupid little rubix cube sized saddle purse won't accommodate it due to being filled by 2 c02 canisters.
My Pendle stays on regardless of how long a ride I'm doing whether it's a trip to the local park with the mutt or a tour. That extra space gives you room to surround your camera with spare clothing.
The straps. Yes they are a faff. They'll start off being stiff when new but will soften up over time. But, unlike a zip, they're unlikely to fail or shatter like some of the nylon clasps.
A proper cotton duck Carradice saddlebag is a one time purchase. Plenty of reports out there of bags being older than their owners and still in good nick.