I have used the Koni-Omega system for years. The lenses, even though produced back in the '70's or earlier, produce superb results; enlargements to 16 x 20 are no problem at all. I use a 58mm, a 90mm, and a 180mm, and they all produce good results. There is also a rather rare 135mm which is occasionally listed on E-Bay; usually the final price is quite high. The strength and weakness of the system involves the backs. On the plus side is the quick interchangeability of magazines--really handy during rapidly-changing events. The negative is that the backs seem to be the mechanical weak point of the system. Faulty film spacing is not unusual with older, well-used backs. Rapid film advance is encouraged by the design, but it's easy to be a little too vigorous and eventually cause some internal damage.
The lock-on sync cords are great--I've never had a failure. The ingenious system of double-exposure prevention, blank- frame prevention interlocks used in changing lenses /magazines, and the sheer sturdiness of the camera are strong assets.
Be aware that there are two different film-back designs. The "flatter" design is less desirable. The "beveled" design is compatible with the interchangeable magazines and will also fit the Koni TLR. It's probably best to get a Rapid M, a 100, or a 200 rather than older models.
The worst thing about the Koni-Omega is that it's no longer being produced; the best things are that it is very durable and there are no batteries in sight! Now, if only someone would tool up to make compatible backs/magazines with the weak points of the design eliminated. . .