I currently have a manfrotto 501 head (cheap, I know).
As I'm out of budget know I was thinking of mounting a ball head (manfrotto 494 rc2) on top of it for fast leveling.
interesting approach. i guess it would technically "work", yes.
wouldnt put more than say a dslr and 135-140max lens on it though...
any more than that and its probably gonna slip
in any case, I must say I haven't worked with any of these gadgets: I'm still stuck with a supercheap tripod and saving for something like a manfrotto 546+501
For still photography I use a Manfrotto 055xpro tripod with a 488 RC4 ball head: when using the DSLR for video I put a 701 pan and tilt head on top (as Norman suggests). Works fine (i.e. is solid with a D7000 and any of the lenses I use for video: Sigma 8-16; Nikon 35; Nikon 18-200) and the bubble levels in the quick release plate of the 488 RC4 head mean levelling is quick. The 488 RC4 head is also useful for connecting, via a qr plate, to my slider. The only pain is that I have to change the quick release plate on the camera when using the 701 head (all my other gear is standardised to the Manfrotto 394/410 qr). Roland
I love it for slider shots as well, especially going from horizontal to diagonal or vertical orientation. It's useless for pans and certainly tilts too. For the price and articulation I'm a big fan of it