It looks like a good idea, but most people won't adjust it to get the proper fill levels. That's why most manufacturers have custom versions of the same company's valves. If you adjust it, it should be a maybe cheaper alternative to the custom valve, but not if you value your time or are paying someone to do it right for you. To maximize water efficiency, you need both the bowl and the tank to fill to the proper level at the same time. If the bowl doesn't get enough water, the next flush will be weak. If the bowl gets too much water, any excess goes down the drain, and wastes water (having nothing to do with the next flush since it is already gone).