The fact that a shop is reputable and employs a manufacturer-certified repairman does not automatically mean that it would be clever to let them touch your regulators. At least not both of them the same month. It is a known fact that some technicians are more "oxygen-compatible" than others (or tech-compatible, or cold-compatible, pick your term). This becomes more of an issue when temperatures or depth or distance to air become extreme. Or if you use oxygen.
Try finding another diveshop and compare the results.
If you want a better regulator set, then do remember that Poseidon Cyklon was introduced half a century ago, and while it has received some technological upgrades in the decades past, it is a great tool favored by many (and hated by some). Apeks DS4 (or the DST with its turret and its extra o-ring) and the ATX/XTX second stage aren't exactly new technology either. Still, they are used in extreme cold and for deep trimix dives and for demanding cave dives. Some Italian regulators have fancy new features aimed at reducing the chance of a freeflow in the extreme cold. I don't need that though, as my cylinders have rotatable rubber knobs that conveniently control air flow

Reliable and well maintained basic technology is all that is needed.
You don't need a 2015 model. The good technology has existed for long. You just need to pick the correct technology, and a good implementation of it, and forget the marketing speeches, and find a truly carefull serviceman.
For cold water you would pick a diaphragm first stage,
such as Apeks DS4 or DST or similar (many other good brands exist; pick one that is easy to service locally). Or you could get a Poseidon Xstream that is great for cold water (approved for use under ice down to -1,6 °C / 29.12 °F without the cold water kit), but possibly hard to get serviced. The HOG is a cheaper copy of Apeks. It is not quite as well manufactured (hence, partially, the price). I have met people complaining about the quality of their HOG: The turret is not quite as stable as the one in Apeks. You get what you pay for, and for some environments good enough is... well... good enough.
The easy answer: Apeks DS4 or DST and XTX50 will not let you down.
DST may have better hose routing with that rotating turret. TEK3 is optimized for doubles. Otherwise they are almost the same product. DIN attachment is sturdy and good.