Before you buy a bunch of new regs (normally you would need 4 total at least, plus one more for your argon bottle if you are talking about cold waters such as the Great Lakes, New England, the USA West Coast, or Northern Europe), you need first to find a reliable service technician locally. This is the person who will take care of your annual re-tunes for these regs. Where I live there are 3 guys who specialize in ScubaPro, one of whom can do almost any brand in addition including Apex.
ScubaPro and Apex are quite widespread world-wide, as are also Zeagle and Atomic in the USA. If you travel and scuba dive, then it makes sense to choose a brand that is widespread in service availability. I have heard of Poseidon (and Oceanic) here and there, but mostly as rentals for basic open water training at scuba stores.
I do not believe there is a performance issue. When you add helium to any other gas mix, it makes the regulator perform better. I believe the salient issue is servicing and parts availability, as well as proper hose routing. But if you do any deep air diving, such as the typical extended range class to 185 fsw (6.6 ATAs), as part of your training, then performance certainly would become an issue. Very few tech divers dive deeper than 100 fsw anymore without helium mixes, however.
Once you find a good, reliable local service tech, you should then ask him for his recommendation for you. Most of your servicing will be done locally. It is rare that anything would be done away from your home base.
You need to see how the hoses coming from the 1st stages can be routed. Normally there needs to be a LP port at the bottom of the 1st stage, going straight down, in order to allow you to properly configure your hoses for your twin tanks and on your deco bottles. Wait for the service tech or your tech instructor to show you how this is supposed to work, before you buy.
I also take at least one extra reg with me (combo of 1st and 2nd stages with a 40 inch hose) anytime I travel. And an extra power inflator and corrugated hose connected together as well, in case that starts to malfunction. I have had both malfunction on trips before. So that makes a minimum of 5 regs (1st & 2nd stages together) plus one more basic 1st stage for the argon bottle.
Buying regs for tech diving is like a new marriage. You hope it will last a lifetime, and it is expensive to give up and then start over. The total cost equals or exceeds most diamond rings! And I am certain that most tech divers keep their regs longer than the average marriage anywhere in the world. So you don't want to be rushing into a purchase like that.
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