I teach both DA buffer and rotary buffing classes here at Meguiar's - I've taught literally hundreds of people how to properly use both tools, so let me put it to you like this:

If I spent 30 minutes with you in a one on one training session on the DA buffer, I would be comfortable letting you buff out my car.

If I spent an entire day with you in a one on one training session on the rotary buffer, I doubt I'd be comfortable turning you loose on your own car.

The learning curves are that different with the two tools. If you use the DA wrong all you do is push product around and you get no results. If you use the rotary wrong you drop your car off at the body shop and pay them to repaint a panel.

That said, the Flex rotary you linked to is their new tool, and I happen to have one. It is, in a nutshell, freakin' incredible. This coming from someone who hates the Flex 3401 forced rotation DA. But I would still caution you against using one.

There are good DA buffers on the market, from Meguiar's G110v2 to the Griot's Garage unit to the Porter Cable 7424XP. They are pretty much all the same (although the 7424XP is a bit down on power compared to the other two) and you can use a wide variety of pads and liquids with them. I'm not all that impressed with the products Griot's makes to go along with the buffer, but there is an awful lot to choose from even if you decide not to go with Meguiar's products.

I wrote a fairly in depth introductory article on using the DA buffer for our forum - you can read it at D/A Buffing 101 – An Introduction to the G110v2 (and similar) - Car Care Forums: Meguiar's Online and it should give you some good insight into how to use the tool for maximum results.