The one thing the
Flex has that none of the others do is...
A VARIABLE TRIGGER !!!!
Plus it can do 9,600 oscillations per minute. That's a ton.
If you want something cheaper and you already own a rotary, perhaps the Dynabrade #61374 Random Orbital Head Kit.
Wrong type of machine, but I wish the little Metabo rotary had a finger-trigger, too.
It would be so much nicer to use and would probably be a bit more popular.