MK21 First Stage
Scubapro has labelled the MK21 as a mid-range first stage. It’s a balanced-piston design with an extremely compact body, made from marine-grade brass with a highly polished chromium-plated finish.
The first stage offers a unique thermal exchange through external fins, which form part of the body’s moulding; the maker claims that this creates optimised freezing resistance.
As standard the first stage has four low- and two high-pressure fixed ports, with the option of a replaceable head that gives a fifth centrally placed low-pressure, high-flow port.
This fifth-port option will be of interest to technical, twin-set or sidemount divers who can maximise their hose-routeing for the best configurations. Scubapro claims that the MK21 is easy to maintain.

G260 Second Stage
The G260 is a balanced, adjustable second stage featuring metal internal components. The body is constructed using high-end plastics with an alloy front cover-locking ring. The diaphragm is larger than you’ll find on most models with a central purge button.
The G260 has Scubapro’s standard adjustable VIVA, with the addition of an inhalation control knob. Hose connections can be reversed to give both left- and right-handed options and, as with the first stage, this gives unlimited options for technical divers when configuring their kit.
High-flow and compact exhaust ports and the maker’s high-flow “Super Comfort” mouthpiece complete the package.

In Use
I was supplied with a MK21 without the fifth-port option, and fitted it with all the usual hoses, plus an electronic transmitter for my Galileo Sol air-integrated computer. I also fitted an analogue gauge for back-up (I really do like to know how much gas I have).
The hp ports are angled slightly upwards, and this created plenty of clearance around the expensive and possibly delicate transmitter.
The lp ports are angled too, allowing the second stage, octopus and inflation hoses to be neatly routed. As is my preference the version I had was fitted with a DIN connector, but 232bar A-clamp connections are also available.
At first glance the G260 seemed a chunky second stage, but under water it felt unobtrusive and light. The purge was easy to find and a delight to operate and delivered air progressively, efficiently clearing any unwanted water without that horrible tonsil-rattling rush experienced with some makes.
I took the set-up down to 30m and put it through the usual test procedures. Inverted it was dry, and when I spat the reg out at depth it didn’t bubble.
I set the inhalation effort control to maximise the airflow and again (this was a first for me with Scubapro regs) it didn’t let out a single bubble either.
The stumpy exhaust ports did push a few bubbles past my face when I was stationary but too few to impair my vision.
I found the cracking pressure (the breathing effort needed to initially open the second-stage valve) to be the least resistant of all the Scubapro regulators I’ve tried, and coupled
with the ease of exhalation the MK21 / G260 combination gave me a breathing experience that was as smooth as silk.

If the MK21 is classed as a mid-range first stage, don’t let that fool you. I found it more than capable, and in fact coupled with the G260 it performed better than most of the top-end models I’ve tested recently.
Compact and lightweight, it gives an excellent hose layout for standard single-cylinder diving, and the addition of the optional fifth port placed centrally should excite the technical divers out there, although I didn’t have the opportunity to test this.
With all regulators sold in the UK having to pass stringent tests to gain the EN250 certification there isn’t that much to choose between them these days, but this one
certainly exceeds the standards in the breathing department, and stood out for me as a top performer.

PRICE £429, optional fifth port head £34
FIRST STAGE Compact, balanced piston
SECOND STAGE Balanced, adjustable
PORTS 4lp, 2hp, optional head for fifth lp.
CONNECTIONS 300bar DIN, 232bar A-clamp
WEIGHT MK21 560g, G260 (with hose) 475g
NITROX Maximum 40% from the box
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