So it only works until they're trained to properly deal with oncoming strikes? If you want to water their eyes, jab them in the nose. If they pull back when getting hit, move in and throw the hook; their jaw is up.
The first application is as a strike to the bridge of the nose. This is where I first started to learn how to use it myself. Waters the other person's eyes pretty quickly and hurts. Alot of people have the reflex (until they train it out) to turn their head when something goes at their face. Also a pull back reaction with their head. this was when I was still pretty new to sparring and so were the people in my class. I found that I would miss a hook, but I could extend my reach with a ridge hand and take advantage of this.
It has the power of a jab with the travel time of a hook and the visibility of a high kick. Sounds like you have all three categories minimized.
Second application - why use a Ridge hand here instead of a hook? simple - it fakes really easily. For alot of reasons a hook is superior in terms of damage. For range though this is great because its often seen to be a straight when instead it comes out a ridge. Its also a bit of a dirty move when done to the side of the head because it just so happens that the jut of your thumb can catch the corner of someone eye...
So you throw a non-power shot near the end of a combo? That seems counterintuitive. Also, you landed it, but to what effect?
the best way to fire a ridge hand is AFTER another strike. In fact it is the common "third" strike in my combo's due to the fact that it takes a very strange line that catches some people unaware. This is not intended as an opener unless you're trying to be tricky somehow that I can't see. This is not a power technique, as opposed to a hook. It can be used against the side of the head to some success but in no way replaces the power of a hook. When I went to the throwdown I was really glad to see that I landed a ridge on about everyone I sparred (nevermind if I got my butt kicked or not). Now,like most techniques, I consider it a tool to be put in a tool box. Just like all tools they have their uses at various times but no one tool can fix it all.