Alkalinity is KH as far as we are concerned, in marine systems and few others, borate contributes to the alkalinity, but for FW, it's all KH.
Poly Phosphates can influence KH in FW also, these are sometimes used to lower pH but they do not add any CO2 obviously.
The Hanna unit you are looking at is a bit pricy. So are the reagents.
I'd just get a decent NO3 test kit, KH, and pH.
I hardly ever test anything anymore.
Most is done by plants, algae, fish appearances/behavior.
Light I'll test more than anything these days.
Then CO2 very carefully.