For the Flex at least, I would also say this:
The coilovers have better damping characteristics (which are adjustable to taste), whereas the H&R springs are great but a little too stiff for the shocks so there's this sensation of the springs working harder than the shocks. It isn't perfectly matched.
Coilovers can get quite a bit lower, or of course you could raise them a bit if you want.
Lastly, the coilovers are of course, also shocks so you're getting new shocks out of the deal.
