I talked to the guy who invented this a few years ago. I got more interested in the liquidator and haven't revisited this product since.
Basically, he drills 4 precise (but different size) holes in a stainless metal disc and you can select your feed rate by choosing the correct hole thru experimentaion. The simplicity is what attracted me to it but (without trying it) it would seem to me to have the following shortcomings
1. I question whether the metering system is precise enough. As jason said, a lot will depend on your particlar pump setup. I'm just not sure the 4 holes will give you what you need.
2. I experimented with some stainless needle valves and found the chlorine ate them up rather quickly. I'm not sure why the same thing wouldn't happen to this.
3. Is there a way to stop the thing from continuing to input chlorine into an IG pool. I don't remember but I think the only way you can stop it is to remove the hose. If so, then you must plug the hose to keep from unpriming the pump.
He may have already solved these problems but, at the time, it didn't seem very practical.