I spend a lotta money over the years on "on the gun" ammo supplies.
However, I've come to the realization that anything added to my gun is just another chunk of weight to deal with.
6 shot side saddles - moving to 4 shot side saddles - to on the buttstock shell caddies - to in the stock (speedfeed) holders.
All of them threw off the balance of the gun, caught on every edge/branch etc....,
In the end, I was always loading the shotgun/holders from boxes of shells.
So my thoughts were what would the best way to grab a box of shells be?
Ended up going with the dedicated SOE Micro Rig
https://www.originalsoegear.com/products/12ga-micro-rig#
In addition to holding a full box of ammo it has fancy Velcro shotgun cards that you can pull from pouches.
You can detach the cards from the pouch and slap it on the side of your shotgun if you are so inclined.
The front of the shell pouch also has Velcro attached to it so you can affix another 2 Velcro shotgun card (slugs) to it as well.
Normal operation is to grab both micro rig and shotgun. Slap either slug or double odd buck stand-alone Velcro card onto shotgun (if you are so inclined).
Peel and stick second card to shotgun and stick depleted SG card onto pouch. If further rounds are needed - feed SG directly from micro rig attached SG cards as required.
If needed, you can stick the flap of the shotgun shell pouch back and directly load from it (more awkward).
Alternatively, if you haven't gone to plan "C" you can, when time permits, reload cards from the pouch that contains box of shells.
Best of both worlds.
YMMV
L