We have an older version of this:
Vacuum for stairs
It does the job - HOWEVER, since we have the cutest, most lovable yellow lab who SHEDS, SHEDS and then SHEDS some more - I don't find that it cleans the "corners" as well as I would like, and, I have to empty the dirt cup 2 or 3 times while vacuuming the stairs. A canister vac would have a huge advantage on the dirt-cup size, although I think it would "lose" an advantage if you can't vacuum from top to bottom without moving the vac.
We have always had an upright - they now have all the tools on board. I have never been "thrilled" at how the uprights do stairs with the on-board tools. the hoses were never long enough, and you still have to deal with the upright.
Now - my grandparents always used to have a canister vac. (Now - granted - this was years, and years, and years ago). The thing they liked about it - when you are vacuuming - you are only moving the hose thingy, the canister is more stationary, so while you are vacuuming, you didn't have the extra weight that you were moving around. (My GP's lived on their own until they were in their late 80's.) The thing they didn't like, but wasn't a huge issue, since their home was pretty small - if you tried to "yank" the canister closer - it would move - but not always the direction you pulled it. It would "yank" the direction that the wheels were pointed in.
Now - I love your plan to get an "upstairs" and a "downstairs" vac. We did that - and I love it. Oh yeah - plus we have the "stairs" vac. And - if we need to do a quick clean - there is one vac for me, one for DH, and one for DD, and the whole house "CAN" get vacuumed in about 15 minutes if needed.
Hope this helps!
Vacuuming the stairs is a nightmare lugging around a heavy upright vacuum and using the hose attachment.
