Firstly, congratulations on your choice of a new sport. I used an Omega II for about 8 years and really loved the performance. The only thing I didn't like about it was that it breathed a little wet, and I found myself having to clear it more than I wanted to. It may have just been a servicing issue, or some small part that might have fixed the situation (diaphram, etc.), but I just got aggravated one day while taking pictures and switched to a very dry breathing reg.
Never had any troubles with freeflowing though. Since you bought it used, I would suggest you have it serviced by a qualified Oceanic technician. He can probably tune it down a little, or replace some inexpensive parts and you should be set. When they work, they work very well. Until you get it serviced, make sure you have the mouthpiece pointed down in the water at the surface, and the front of the reg where the diaphram is pointed up towards the sky. When you have it tuned, don't have it tuned down so much as to make it too hard to breathe from. Your tech will know where to find the compromise between free flow and ease of breathing.
I never realized how loud my bubbles were going past my ears until I stopped using the Omega II. It definitely has some great advantages by being a side breather. You can see better and hear better, and it delivers a comfortable amount of air volume. There are much easier breathing regs out there because the Omega II works on a servo valve, which opens the main valve to deliver air to you on demand. This "two step" process can sometimes be felt by divers who have used several types of regs, but you may never notice the difference.
I am no regulator expert or technician by any stretch of the imagination, but I will try to explain the servo concept. You can find many good threads on this board giving much better descriptions than this one, so try a search. The servo valve arrangement has a negative point being that it is not a "fail safe/fail open" downstream valve system. It is an upstream design. If there is a problem and the servo valve doesn't open, then air supply may be shut off to the diver, instead of the 2nd stage freeflowing. However, modern reg designs are so good that I have never heard of this happening, and I have done many dives with the Omega II. Also, Oceanic regs are almost "bullet proof" and offer years of service and reliability if cared for properly and serviced. They are a great value for the money too. Even the PX2 you have is a workhorse piston design that delivers plenty of air flow.
So, in summary...
Not so good points: wet breather, upstream design, satisfactory breather (not the best), yours needs servicing.
Good points: no bubbles in your field of vision, quieter, streamlined, no jaw fatigue, no right side up (can be used as an octo with the purge valve/diaphram on the left or right side of your buddy's mouth), easy to get parts and service, inexpensive.
Even though I haven't used mine as my primary 2nd stage in over a year, I still use one as an octo (and have another as a backup). Still can't let go of those things!
Finally...you should have yours inspected and serviced. As a new diver, you're going to have issues with air consumption for a while (not to mention buoyancy control-another topic), but remember you can use your snorkel on the surface to conserve air if the surface is calm enough. Hope this helps, and I hope others will follow and give better explanations of the design. Be safe and happy diving.
