I started using a N26K tank last year and am very happy. As for downsides, I don’t really have any. Depending on your luck with compressors, you could argue that it could be cheaper or more expensive, depending on your situation. It is heavy, but you shouldn’t have to move it. My dealer doesn’t deliver to my residential area, but they are right down the road from my office. When I need a new one, I pull it up on my utility trailer, take it down there, and bring it back home. I do keep it on a small cart to move it around easier.
My rental is $75 a year, and $75 to fill it. Took me just over a year to need a fill. I fill to a bottle, and then to my rifle, until the tank gets low and then I fill straight to the gun.