The make up of the Omnicraft GT-4A is pretty simple, as each channel only has a limited amount of parameters. It doesn't limit what you can do with it, as this can definitely do the job well of gating. The parameters that each of the four channels has are for threshold, range, and release. Even if you aren't too familiar with how to use a gate, you should be able to figure out how to use this without the help of a manual.
The Omnicraft GT-4A won't color your sound as far as I can tell, which is really all that you can ask for from a gate. While gates aren't really necessary with modern day recording technology, but if you're going old school to tape or something like that, it can definitely be a benefit to have something like this around. Even if you want to gate with your DAW, this can certainly do the trick. It's definitely most useful for tracking drums...
I can't say that this is a superior four channel gate, but it definitely does the job. It seems like you'd be able to get one of these pretty cheap since not too many people are using gates any more. There doesn't seem to be too much information out there about the Omnicraft GT-4A, but the good news is that if you do come across one, it's pretty clear exactly what it does and how to use it. If you need a gate, you'll definitely get some bang for your buck with the GT-4A if you can find one.