Just curious why you think that. Is it because of price....higher = better, sales hype or what?
Price has very little to do with performance.
Piston regs, which the MK-25 is, are less well suited for cold water use, not saying they will not work but why bother with the less advantageous model? Sealing them (any piston reg for that matter) is a messy pain as opposed to a diaphragm reg (MK-17) which is easily sealed.
It is true a MK-25 will flow a lot more gas than a MK-17 or any diaphragm reg for that matter but so what? The tank valve can not flow as much as pretty much any modern reg and even if it could, 2 of the best second stages available can not flow anywhere near the amount of gas that pretty much any low end modern first stage can flow so why spend money on a high end first stage that does nothing for you ...except clean out your wallet? What you need to understand is 99% of the performance of any reg is determined by the second stage. As long as a first stage can flow more gas than the second stage it's hooked to and can keep IP reasonably constant, which pretty much any modern first stage can do, then the second stage determines the performance of the reg assembly. In other words, a low end first stage coupled with a good quality second stage will work great but a poor quality second stage hooked to the best high end first stage will still perform poorly. While on the subject, there is little to be gained by buying the top end second stage as well. Most all of them are simply the upper mid range seconds of the manufactures line with flashy do dads added. Most don't do much of anything but increase the bling factor and cost money.
If you are diving cold water, get a sealed diaphragm first stage (for warm water is doesn't matter at all) and couple that with a mid to upper mid range second stage. This will give you almost identical performance as a fully loaded top of the line reg at a much lower price point.
