The Mares 25XR 1st stage is designed/intended by Mares to be used in tandem in a tech/twinset configuration.
Personally I think this is a stupid design as it makes for a very limiting design with regards to equipment configuration unless one ONLY dives a double tank or H/Y valve setup.
Your desire to swap this between tech and single tank recreational setup makes this a poor choice for what you want to do.
Also, The DFC and vortex features look good on paper but in reality, in my opinion, are just design gimmicks that Mares has stuck with over the years, they use those features to differentiate themselves from the rest of the market but any advantage is really only realized under testing/laboratory conditions, in the real world, a diver will not realize any difference but it makes a good discussion point from a salesman point of view. Full disclaimer, i dive with a pair of old Mares MR22s that have the DVC and the Abyss 2nd stages have the vortex tube feature as well....I can't tell a difference between my regs and the aqualung titans one of my clubs stock or my wife's calypso reg set.
One nice thing about Mares is that they are simple/straight forward to service if one is looking to service them oneself, at least the MR22 is, the only issue is it can be a struggle to find parts for self-service.
The Deep6 regs come with a service kit so 2 years or so down the road you will have the parts already on hand for overhaul....that will give you a total of 4-6 years of service life before you will need to find parts again. If you are living in a place where getting parts from Deep6 will be a problem then you can call them to discuss what in their parts kit would be interchangeable with common parts found in other regulator parts kit....for instance, the high pressure poppet for the Mares MR22 and MR52 is relatively interchangeable with the high pressure poppet speced for some Aqualung regulators, and is readily available from Trident for shops to purchase.
Mares makes some good stuff...but being that they are an Italian company, they seem to take a well engineered product and then jack it up by prioritizing some aspect of form factor instead of function. I was just discussing this with an Italian colleague (I live in Belgium), and he agrees that the Italian mentality is in favor of something "new" every year. For skis, the companies will take last years product and put new caps on them to change the color scheme and call it new. For regulators the companies make some minor change to the exterior and hype it as new and better. I have seen it in the ski, diving, and cycling industries with Italian designed/made components...and I am sure it happens in the auto industry as well.
-Z