An important point that must be remembered is that a more expensive price tag does not necessarily equate a better performing regulator. For example, the Atomic Z1 offers identical performance parameters to the vastly more expensive Tx1. The Apeks line follows the same pattern with the various first stages all delivering virtually the same gas flow. There are the "bells and whistles" that many divers prefer on a reg. A number of these, such as inhalation effort controls and venturi adjustments certainly have their place and respective value. Expensive alloys and cosmetics are there for the same reason that expensive Italian suits exist...prestige.
I use and am extremely pleased with the performance of my Mares regulators. I have used them for so long and have serviced so darn many that I can tune them to meet the needs of 90%(+) of the world's divers. Adjustable inhalation second stages can be user tuned to deliver virtually zero inhalation effort, but at the price of increased mechanical complexity and slightly decreased reliability. To each his own....
Purchase a high quality reg and care for it properly. It is very tough to go wrong with a major brand model.
I worked for Rodale's Scuba Diving Magazine for a few years and had a hand in the regulator tests. Any reg that can pass US Navy Class A standards is certainly up to the challenge of the vast majority of divers that I have had the pleasure of knowing. 27 years and counting has enabled me to form a few viewpoints on regs and their design parameters. My background is secondary science education, so I've always had a technical interest in the mechanical factors in a reg's design and funtioning. Divers have never had it so good! I wouldn't want to go back to the regs of yesterday that didn't offer any form of venturi assist or vast gas flow from a balanced first stage. I've drawn air from many vintage regs, and still enjoy making vintage dives. Yet, when I am making a dive in excess of 40' or so, a modern model is serving my needs.
Choose a reg that meets your needs and keep it in pristine condition.
Safe diving!
Greg