Don't underestimate the value of installation.
They aren't complicated but they are heavy.
+1 on the weight! They are extremely heavy. I had my 4 post installed by a local shop, even though I ordered the lift from out of state.
Side note - you can order and have lifts delivered unassembled; HOWEVER, most manufacturers will only deliver to a loading dock of some sort, given the packaging, etc. So, I couldn't have the setup delivered directly to my home - I had to have mine delivered to the local shop setting the lift up.
I, too, have a very limited interior garage height. I thought I had 10' ceilings; which would have been great. However, my ceiling is 9' 4" a the lowest point. I was able to make the lift work, but much like Bob G mentioned, it really depends on what you have underneath AND on top.
Another issue to tackle is not just the over and under space, but you also need to figure out upper and lower clearances based on the manual locking slots. And, you also have to give yourself at least an additional 3 inches once the lift is resting on the locks, as you'll need about 3 inches to raise the lift to off the locks to release the locks and then lower the upper car. I remedied this by measuring everything ahead of time (you an go online and find the heights at which the locks will set), and I ended up having 3/4" thick aluminum cut to the size of the post feet and placed under the post feet to allow the exact height required above and below.
Hope this helps!