Couple of reasons why the hydraulics won out for small studio work.
(A) at least in the states, screw (fly) presses are hard to find
outside the north-east corridor. (Much easier in the UK, I'm given
to understand.) (B) screw presses are heavy and a pain in the tail to
move. Equivalent tonnage hydraulic presses are about 1/5th the
(Trust me on this, I used to own a giant fly press. It broke the
driveway when I brought it home.) (PS. > I wish to publicly ...) (C)
manual hydraulics don't hit with the same effective force, but they
do have the major advantage that if you get a finger caught
somewhere, it's very easy to *STOP PUMPING*. A screw press would
just smash your finger.
(D) once you get into more advanced things like deep draw kits,
punches and bending/breaking dies, you can do those with your hands
in the press (see point C) so that you can guide/examine the work as
it happens, where you simply couldn't do that with a faster acting
press. (E) thanks to the efforts of Lee Marshall and Phil Porier of
Bonny Doon Presses, there's a wide range of easily available tooling
for the hydraulics, so that you don't have to spend half your time
machining up the tools to make the work before you even get started.
(disclosure: I work with Lee, and Phil's a friend, so I'm hardly
Screw presses do have the advantage that they dump a lot of energy
into the work piece in a very short time, which lets them move it
much further, much faster than the slow 'squeeeeeeeeze' of a
hydraulic can, but for most people, with most work, that advantage
doesn't make it worth the effort to scrounge one up, or tool it up
once they've found it. (I sold mine, and I *do* have the gear to tool
it up, if that tells you anything.) (If you want to see pictures of
the biggest screw press I've ever seen, and the fun and joy I had
dragging its frozen carcass out of a half demolished warehouse in
Detroit, the whole sordid saga is laid out here:
Hope that was of some use.