The systainers were a pleasant surprise when I discovered Festool. My dream is for a global ISO standard for a system of small containers/totes. So far the world hasn't standardized a container smaller than a 20 foot conex.
As it is, what Festool has is the closest thing to getting it right. I own a lot of power tools, but the problem is of course with other brands you either don't get any case (really bad), or as is often the case they make a different case for every tool, everyone a different size and shape. I'm sure many folks have the random pile of Milwaukee tool blow molded cases piled in the corner always wanting to fall over. And then the random pile of all the tools that never had a case, or the really sad cardboard box, maybe a bunch of the insanely pointless canvases bag (seriously, why not just cut to the chase and have them connect as a filter bag in a shop vac so they are useful). I have most my life stored in rubber totes because of moving around. It's nice, just move stuff around with hand trucks, but they are not a good answer. Lots of various tools, materials, etc get stored in Bins in a shelf system, not a great solution either. Having everything in something like the festool systainers is the much better solution. Biggest issue with converting tools over to them would be the cases they came with, can't throw them out as now that sucks if you go to sell them, yet they take up space and don't stack nice.
I would agree that they aren't going to be the fastest answer, but when you need to keep everything stored away, because either you go to a jobsite, or like me, you move around a lot, you have small shop space, you have a house under construction for years, etc. Having a way to put everything away nicely that stacks nicely, or can have nice standardized cabinetry built for it is great. Moving is so much easier when you keep all your belongings in totes/containers and just point to movers and they move it. Also as people mentioned being able to put the tools away from dust and everything else is nice. Means tearing tools down for maintenance cleaning less often. Not having accessories scattered around with no home. Having a place for accessories in the case with the tool. The key to managing small spaces is storage. A Systainer may seam big or wasteful, but it's actually a very efficient way to do it. Shelves with scattered and tangled tools take up more room, random sized cases package less efficiently than standard module based cases. People don't need bigger houses or garages, they need better planned storage.
Such cases also cause manufactures to think thru the design a little bit. Try harder to fit into the same size case as the other stuff. Some stuff will never happen, I love that my Bosch table saw basically packs up into a cube. If they made a form fit case it dropped into, even better. I would love to see a 12" compound miter saw that could do the same.
I have too many tools that lay around with no good way to store them. I grew up with tools jammed under the workbench getting covered in everything in the garage, I don't want that again.
They could certainly make a better container, but even a less ideal container that is standardized is better than chaos.
Pretty sure if someone with a vacuum former started making plastic inserts for systainers for Milwaukee, Bosch, Dewalt tools they would have no problem selling them to folks.
