Agreed - the ultra low range kit which measures phosphorus in ppb (736) is the one to get if you're really trying to control phosphates down to the nubbins. (I'd argue you have bigger problems than which kit to choose if your phosphate is so high you need to worry about it, but...)
The other kit is nice as well, and you will still get nice consistent results, but it's accuracy is limited down in the range where we'd really care about it - still better, but almost like the drip tests.
Personally, I've never had a problem judging nutrient levels by rate and quantity of algae growth - especially on the aquarium glass. And I manage my livestock levels smartly so the tank never gets overwhelmed. Part of the KISS theory of reefkeeping. No PO4 kits, no GFO or carbon reactors, no carbon dosing, etc, etc, etc.
If you have only moderate algae growth (majority hopefully on the glass) and aren't already overstocked, I don't see why this couldn't work for you as well.
Hope this helps!
-Matt
P.S. I would probably stick with Chemipure
Elite if you do use a chemical media to remove phosphates. For small problems, it's a very convenient blend of carbon and GFO (and some DI resin that's irrelevant in saltwater), and probably more gentle than an aluminum-based product. You may be using too small an amount of GFO in this scenario for this to be noticeable, but be aware than GFO does have a depressive effect on alkalinity. (Not sure this actually effects alkalinity or just the test, so I wouldn't necessarily do anything about any change you see....just be aware.)
