I found the Phottix Cleon to be a real bargain at ~$37 with shipping off eBay from China. I got one with a molded 10-pin Nikon plug that has the locknut retainer, and would have gladly paid as much for the plug end alone. I modified mine by splicing in a 1/8" (3.5mm) stereo in line jack and plug so that I can use it with any and all of my electrically triggered cameras. One issue to note however, is the slight but noticeable time lag with this Cleon release, perhaps on the order of a 1/8 sec. If this is critical you may want to investigate using a Pocket Wizard transceiver pair instead.

The two-stage triggers do a nice job of waking up your camera's metering from sleep as would a half depress of the shutter release-- but you may not even have to use it with your OM-1.