IME API hasn't failed me in the last 15 years and I test weekly even though my parameters rarely change much.
I've only used Seachem MultiTest Phosphate
test because I wanted to verify a lower reading then AP's test (lowest is .25 ppm
for AP and .05 for SeaChem) and it works like a charm.
Most test kits on the market do a decent job but keep in mind that all can expire and will give false readings over time (typically 1-2 years) so IMO
it's best to buy online which usually will ensure fresher stock (and cheaper) then one that might sit on a lfs
self for 6+ months before being bought.