Notably, 10 years ago I could swap a butane or propane tank from one vendor with one of another vendor at any place that sold butane/propane.

The last time I tried to do that (6 months ago) they rejected it. I had to go to the original supplier, as they were no longer refilling each others branded containers. In spite of standard fittings/sizes/etc. They've become significantly less fungible, and I can no longer just go to the nearest or cheapest supplier based on my needs.

Even worse, I've just realised that I now effectively have two un-refillable tanks, as Homebase just shut down all my local branches. Which I paid deposits on when I bought them, obviously. Nice ...

uhaul will generally fill propane tanks. When you swap tanks you get substantially less than what uhaul will fill to.

Yep. They also over-charge for propane, sell the tanks not fully-filled, and don't compensate you for propane left in the tanks when you return them. All to increase convenience slightly (I can get the swap tanks at the supermarket or Home Depot, but I have to go to a specific gas station to fill the tanks I own). I strongly prefer the non-swap solution.

It works almost the same for bottled oxy/fuel/shielding gas used for cutting and welding operations across the country.