For a 90mm F2.8 lens, the Tamron macro isn't terribly big. I use it handheld for macros all the time. It also has a AF/MF clutch that is easily engaged by pulling or pushing the focus ring.
Like JeffJS above, I find AF to be more hindrance than help on macro photography. For me, one of the big challenges of macro photography is what is left OOF as much as what is in focus. That means I have to decide where the focus should go. In addition,
focus stacking intro here a great tool for macro photography, is a lot easier with MF.
I'd also like to plug the Raynox clip on diopters. They work quite well and certainly get close enough, in addition you don't need to change lenses, just clip it on the front of what ever lens is mounted on your camera. For many examples of what they can accomplish check out the Raynox Macro club over in the Lens Club forum.
NaCl(macros can be fun)H2O