A friend has offered to sell me his regulator. It's a US Divers model (don't have the model number yet) that was supposedly top-of-the-line when he bought it. I plan to take it to my local dive shop for reconditioning. Does it make sense to purchase a good used regulator rather than a new model? I'm wondering whether regulators have gone through significant technical improvement say in the last 5 to 10 years.