I wouldn't waste the money. I've used that before, and was not impressed at all. It didn't work--it hardly got any of the hard water deposits off, even with soaking and lots of elbow grease. I used most of a bottle with little results.
If you can't reduce the amount of surface agitation to avoid having deposits develop, try using something like oxyclean. You don't want to get it in the tank, but it works. You can mix up water and oxyclean and use a rag to get most of it off pretty quickly--better if you use hot water.
I've had decent results using a few of the orange cleaner products as well--and they are easier to apply.
I still use a razor blade when removing stains from the inside of the tank. The sprays and soaked rags are fine for outside stuff, and you can easily soak equipment. I just worry about dropping my rag into my tank, no matter what is on it.