The original Omega used a Springfield Armory 1911 frame and a Peters-Stahl slide & barrel. This is a small West German company. The slide/barrel is called "linkless", as it does away with the little pivoting link as used on all 1911 pistols. It has a ramp/cam arrangement which locks & unlocks the barrel during the firing cycle.
This supposedly allows much higher-pressure ammo to be chambered in the 1911 frame. The barrel also does not have the "ridges" which lock into the slide as on a 1911, but a large rectangular block, similar to that seen on SIG-SAUER barrels.
The pistols were all initially chambered in 10mm auto. They were sold in 5" and 6" barrel lengths, ported or unported. The porting is two oval slots cut through the slide & barrel on either side of the front sight blade. It works great. The ported 10mm is as easy to shoot as a .45 acp.
I assume that the target market for the Omega was high-end sporting/target/defensive use. I'll bet it was too expensive for military or police contracts.
After being discontinued for reasons I do not know, it was re-issued by Springfield Armory about four years later, and then discontinued again. I understand that the re-issued versions were available with optional interchangeable barrels in 9mm, .38 super, 10mm, and .45 acp. I've never seen one of these multi-caliber versions.
I'm sure one of the negatives was the high price. When I bought mine, it was $800 - very steep for a production piece! I assume the re-issued version was expensive as well, particularly with extra barrels & mags. The price, along with likely difficulties in delivery of the Peters-Stahl upper assembly, are probably the main reasons for it's demise.
A minor problem I encountered was that the 10mm Springfield mags were no good at all. A switch to Colt mags solved the problem.
The pistol is exceedingly accurate and easy to shoot. It never jams. I had a trigger job done at King's Works to improve the trigger pull, which was worth it. I understand that King's will provide alternate barrels in .40 S&W, .357SIG, and other popular calibers, as the mechanism apparently likes most rounds! I'm considering getting these two new barrels for the heck of it.
If you can find one at a gun show or a gun dealer, I think you will be pleased with the Omega. Good luck!
A couple of other points about the Omega.
The earlier models only had one extractor, these supposedly had a lot of problems with jamming. There was also a problem with the guide rod and firing pins not being properly heat treated. They would break.
Mine is a 6" ported model in 10mm with the twin extractors and jammed constantly until I put in a lighter recoil spring. As I bought it used (no manual) I have no idea if the current spring is lighter than stock, however.
I have heard that a company called Harris-McMillan is now importing the Stahls' upper. They supposedly also have the barrels for the other calibers (.38 super, .40S&W, 10mm and 45 ACP, I think. (One of the features of the Omega/Stahls design is that you can change calibers with only a barrel switch, the slide stays the same)