Test kit... Cheaper in the long run
I wish I could offer a clean, easy answer — I have the same question. I keep reading too, that the test strips are "inaccurate". My LFS
also tells me not to trust the strips.
Economics-wise, if I'd bought the API test kit from the beginning (over a year ago) as opposed to the test strips, I'd be ahead in the dollars and cents game. Test kit is cheaper in the long run — and likely, more accurate.
In the mean time, I bring a bottle of my tank water to my LFS
for a test, about once per month. I haven't worn-out my welcome — yet.
Four Zebra Danio; 2 Tiger Barbs. Aquarium is approx. 2 years. 29 gal freshwater; Fluval 206 (bio-mech/ammo-carb/polisher), Whisper 40 air; Current Freshwater LED. 4 Anubis plants (various sizes); one small drift wood log. Pea gravel substrate, approx. 1-1/2" deep. Avrg. Chems: Ammo=0, Rates=10ppm, Rites=0, pH=7.0, Temp=78degF