Pros: Metal construction, easy parts availability
Cons: Metal construction, you'll need those parts
First of all, I love my Miele (see my review). When I vacuum this is the machine I use, and love. I had a 'commercial' Panasonic upright that I bought in the late 80's. However, my cleaning lady, who I swear was half gorilla, somehow managed to keep breaking the thing. After several trips to the shop and a rebuild, I wanted to find something sufficiently sturdy that she couldn't break it. I found a mint condition Heritage II at a local vacuum shop.
The first vacuum I bought for myself back in the 70's was a Kirby from the 50's, and I still have it. I seldom use it because it has the old nasty cloth bag with the scraper inside instead of replaceable bags. I promise the thing sends out more dust than it vacuums up!
The Heritage II must be one of the heaviest vacuum cleaners ever made. It weighs about as much as my Rug Doctor! Heaven help you if you don't have the height adjustment set too low for your carpet--it'll rupture a disc in your back. You learn in a hurry what settings to use in your own home.
On the plus side, my cleaning lady met her match with this machine. Unlike so many other Kirby owners, I haven't had to replace a bunch of belts. With its all-metal body surrounded by rubber, she could ram the thing into furniture all day long and not hurt it. When the shiny metal body gets dim looking a little silver polish on a cloth will restore the finish.
Unfortunately, Kirby has never updated its antique design, and consequently still sucks everything through its fan in the old 'dirty motor' style. A coin can, and will, break the fan before you can do anything about it. Not a really expensive repair unless you start doing it quite often, which happened to me. I'd never buy a new machine with this design--it's just a stupid and unnecessary way to build vacuums now.
The biggest drawback, though, is that with this old-fashioned design, no matter how well the bags filter the air, the motor itself spews out carbon dust into the air, as it has no filtering at all! I saw a vacuum cleaner test on TV a couple of years ago, and while the current Kirby filtered fairly well with the bag, the motor discharged just about as much crud right back into the air! This isn't unique to Kirby; Rainbow and Filter Queen both do the same thing. Newer designs, like my Miele canister, can't do this because the sealed body also filters the motor exhaust. If you want to confuse a Kirby salesman, ask him about this--there is no solution to this with Kirby's design.
After several years and several fan replacements, I ended up switching cleaning ladies, and the Kirby just sits in the closet most of the time now. If I feel nostalgic I'll take it out and vacuum a little just to remind me what that old 'just vacuumed' odor smells like! Certainly whenever one of my relatives wants to borrow a vacuum the Kirby is the one I loan out.
Owning a Kirby, even in mint condition, is like owning a car from the 30's. It reminds you in a hurry of the progress made in this industry , and that vacuum cleaners don't need 'road hugging' weight to do a superior job!