I had a look at the second type of regulator - it's described as a Bleed type regulator:
1/4" BSP Swivel nut air inlet to attach to compressor
1/8" BSP Male outlet to attach suitable airhose
100 PSI (7 BAR) Pressure gauge
50 micron filter to remove particulates and moisture from air supply
One-touch water drain
Bleed type regulator to reduce pressure
I assume it must vent air to stop some kind of back pressure building up against the diaphragm in the compressor or something. I just wondered why it seemed to mention this specifically with the Werther Compressor I purchased - maybe it's just a bit pony - might cause it to overheat or something if the airflow is restricted or something?
I also found this when I was looking for more info online, this compressor has internal bleeding - Can anyone help clarify what all this means? I'm sure it'd pretty much work by just screwing a regulator on the outlet but it's nice to understand why some things work and others work better:
CYCLONE I MODEL 180-1 
Portable 1/12 HP oil-less diaphragm type compressor has internal bleed,
allowing use with any make air brush. It is compact, lightweight and quiet
and can be carried form room to room. Maximum running pressure Approx.
28 PSI. (1.93 bar)
Additional Specifications:
Motor: 115 volts, 60 Hz, 2.5 amp
Dimensions: 8 ¼” L X 4 ¾” W X 7” H (21 X 12 X 18 cm)
Shipping Weight: 9 lbs (4.08 kg).
22.5L/min @ 1.38 bar