I recently got back from a bike packing event in the Netherlands and there were a plethora of set ups. Tailfin featured very heavily indeed. Aside from the seat packs, lots of tailfin frame bags too.
The only negative I heard about the tailfin seat pack was chatting to one rider who said his bike felt unstable descending at speed. To be fair that could have been more about his bike geo.
Personally Im not a fan of under seat roll bags (windsock type affairs) and favour a Carradice type seat bag on a frame.
I use this one.
https://builtbyswift.com/shop/zeitgeist-pack/Ive had some revelate frame bags for quite a few years that have had a hard life and they are still in great shape. Overbuilt zips etc. They are really well constructed. it's a shame they are only black or battleship grey.
I have a sunlite trunk bag that I like to use a lot too. It's got fold away side pockets and a bungee to stash stuff on the top. It's easily taken on and off pannier frame with velcro. It's not very water resistant.
I have an arkel trunk bag too thats similar very neat but find its too small for most of my trips.
I use front panniers over rear generally as the bike feels really stable that way.
By far my favourite bag right now is a Gramm diamond bag. It needs a front rack though. It's a really neat bit of kit, very compact but big enough to stash a fair bit of stuff. There is even a rear portal for wires to stash electrical gear. I actually switched out our big Rando bags that were pretty cumbersome for these bags as they are so good.
Gramm made me some custom bags for my gravel bike too which are fabulous.
image of the bags here.
https://www.instagram.com/p/CqGMOmTOynL/?img_index=1If you are touring heavy, and have the toe clearance, the old ortlieb roll top panniers are great.
We used to and like the ortlieb bar bags as well with the click fix attachment (a bit fiddly) but TBH with the Gramm diamond bags I can't see ever fitting them again. The later versions with magnets for closing the lid are pretty cool.