They are Aluminum and they look like they are a good replacement for the M212 Nylon cases? Has anyone tried them?

Yes.

With hotter loads they seem to last fewer firings than nylon weirdly - unless you blew out the nose of the high pressure chamber.

The aluminum seems to stretch fairly readily.

I think the smaller low pressure chamber in them causes the need for reduced powder charges.

Havent used any myself yet but will be picking some up.

Guessing not worth buying them over the Nylon cases? Since they cost more. (If you can find any Nylon cases anymore)

If you are referring to the green anodized ones, I love them for reloading. They are easy to reload, hold enough Bullseye to do the job, and the vent plugs are easy to replace. I use a bit of cotton string to fit that closing plug (the piece with the primer) in place. To reload them, replace the primer, replace the vent hole burst disc, load your charge, hold the cotton string (about the thickness of one of the inner strands of 550 cord) (you could use an inner strand of 550 cord…) on one side of the plug and start it in the casing. The string will make the plug fit tight and not back out after you load it.

The powder charge will depend on the weight and type of projectile. 3 grains (reloading scale) of Bullseye is good for rubber batons. 6-7 grains for 781 projectiles. 5 for pyro air or ground rounds where you are lighting fuse with your launch. GROG

I think I'm thinking of a different product entirely! The type I'm thinking of have plain aluminum and black lettering and use the usual blank.

Picked up some to test. I had one i used for a buckshot test round, but a .38BLP gave the pressure chamber a prolapse. Luckily I was able to drill it out and salvage the case.

As others have said, the mouth of the casing where the projectile seats will expand. With enough sealant around the projectile, I haven't found this to be an issue. No further expansion after the first firing. I have 10 reloads on some.