Hey Ron, The ABD is a diaphram type compressor as is many hobby types.
To get a piston compressor you're talking more money and much more
noise, also they won't be listed as oil-less. For a hobby compressor
the 1/8 hp is fine. The tank is around 3/4 of a gallon (.7, I think).
It is pretty much the same thing as this compressor -
#121TK at Airbrush City.
For doing the occasional spray painting of models the compressor is
more than adequate. My wife has been playing around doing T-shirts and
painting on canvas spraying at 50 - 60 psi with my BCS. For modeling
it's been down around 15 - 25 psi depending on what I've been doing.
The air tank doesn't seem big enough, but it is. All it really needs to
do is prevent the pulsation from the compressor and give enough of a
reserve to allow the motor to turn off once and awhile. If you were
going to do any kind of production spraying where the compressor would
be going non-stop, then I'd recommend getting an appropriate compressor
(such as a garage type) as this wouldn't last for that like any hobby
compressor wouldn't.
Not that I'm an expert on compressors, but I still have my old garage
compressor from when I owned my business. I bought the ABD after
testing a lot of compressors looking for a quiet one for use in the
house during those long cold winter months. It ended up being the
quitest and also had the most power, best part is it wasn't overly
expensive either.
-- EDIT --
I'm assuming it's a diaphram type compressor. Nothing is mentioned in
the documentation and I haven't taken it apart yet. It is oil-less, so
it leads me to believe it is.