I care less what you buy, I posted my response to try and answer some question. But that said, I find it very hard to sit back and listen to others that suggest stupid acts like using the lift, 2 or 4-post in a manor that it was never designed for. I would never use a 2-post lift to pull an engine, if your to tight to spend on a engine lift then leave it for some that is way more qualified and reasonable. Also, the commits about installing a lift in a concert floor that is less then the manufacturers suggestion and then bracing the top of the lift to the ceiling, is plain stupidity at it's highest level.
What you do is your business, until it becomes so crazy that it can effect others unaware of your exploits. It your going to buy anything, install it as it should be installed. You guy's are so far out there I have to wonder how you got this far in life, I only hope it didn't include killing or Manning anyone else. I can't imagine using my lift on a normal 4" floor. Sorry this is just to extreme for me. I might have gone overboard when we built the shop, buy digging out that area, in a large 8 foot square area and making it 18" thick. BUT, I don't have to worry about killing anyone either. What difference does the quality of lift you buy, when you install it wrong.
I usually don't get up-set at the many idiot that tend to hang around some sites like this, but you are simply putting out very dangerous information, to those two simple to read there instructions. Do a search, there are plenty of home lifts that fail, and the number one reason is just as you may think, improper installations. A long time ago, I had the great pleasure is trying to save a young man that was pinned under a car. He was exceedingly stupid and never educated himself or maybe didn't care, about how to properly use jack stands and work underneath a car. Yes, there was nothing I could do for him, except watch as the weight of the car, slowly crushed him to death. The really sad part wa the horrified look in the face of the man' son and wife. I will never forget that day or the horrible sounds he made while he passed from this life to what lies beyond. I'm sure that kid will be marred for life.