I have a question about BM vs SM and how it is better for your knees? Weight is weight so as long as you are carrying that weight above your knees, your knees see the same amount of weight? I've seen this come up several time in SM discussions and I don't get it but I do understand it places the weight differently but it is still weight above the knees.
Currently I’m quarry/lake diving with walk in entrances. I put my SM tanks on in the water. I’m not walking distances with doubles on my back. The 50s are light enough I can actually walk them out of the water after the second dive with tanks clipped to me. If I don’t want to carry my HP80s to the water, I roll them in a cart. My knees are much happier now. They used to hurt just from walking my doubles around at the quarry.
I see a number of older folks who use SM for quarry diving and they always roll their tanks down to the water.