I've used Salifert exclusively for over 30 years. Reasonably priced, easy to use, repeatable results.
And FWIW - I wouldn't waste a dime on a pH checker - it's a number that just does not mean all that much in a marine tank. Concentrate on Salinity, temp, Nitrate, Phosphate, and if you keep stony corals, Calcium, Alkalinity, and Magnesium.