? what is the difference between an expensive or nonexplosive reg?
Expensive regs cost a lot.
Non-explosive regs...well...errrr...don't explode. I suppose that nonexplosive regs could be either expensive or inexpensive.
If you're asking about the difference between an expensive reg (top-of-the-line) and a more modestly priced reg in the middle of the line from a given manufacturer...there will be features that vary and this may/may not significantly affect performance.
I would recommend that you rent regs for a few post-certification dives in order to get some experience with using different brands/models of regs. You'll find that you might like how compact/lightweight a reg is (good for traveling), how "natural" breathing from it feels, whether it has an inhalation adjustment knob on the side, or whether your exhaust bubbles are deflected properly away from your field of vision.
An important thing to do
before making your reg purchase is to ensure that a trustworthy local reg tech can service it for you.
Reg tuning can make a
world of difference in breathing performance. An expensive reg can under-perform if it's tuned improperly or requires servicing. The reality of the situation is that often middle-of-the-road regs can be tuned/serviced to perform pretty darn well by a competent reg tech.
Some reg manufacturers will try to distinguish their offerings by providing a "lifetime warranty" which includes the cost of overhaul parts. One still has to pay for the labor associated with cleaning the chrome parts and installing the o-rings/seats in the overhaul kit. The free-overhaul-parts-for-life policy (provided you service the regs on a manufacturer-specified timetable) may or may not be a good deal in the long run. Some people are comfortable stretching out the recommended interval by performing more frequent functional reg checks on their own. This usually results in voiding the free-overhaul-parts-for-life, but they still might save a few bucks in the long run. Others will purchase the overhaul kits and do a DIY overhaul. The vast majority of divers regard the reg setup as a magical "black box" that is "life support" equipment and should only be cleaned/adjusted by a pro. For a beginner diver making a first reg purchase, it's probably best to find a good reg tech and have him do the reg overhauls according to the manufacturer-recommended interval.
In most cases, buying a used regulator makes a lot of sense if you know how to service it yourself. If you are considering buying a used reg setup and you lack the knowledge to assess the value/condition of the gear, then take it to an honest, competent reg tech in your local area before making the purchase. You should learn how much it will cost to get the reg into a dive-able condition. The cost of labor and overhaul parts may surprise you. Add the servicing cost to the seller's advertised price and compare that number to how much a new reg setup costs. Understand that, in general, the original manufacturer's warranty is non-transferable to secondhand buyers.
