As for the checker, yes they are similar to the unit that you have or had before and yes the price is much better. Ultimately that is what has made them so popular now.
The digital refract is specifically for salinity and it does not check any other parameters in the water such as pH, alk etc.
I use one of these for checking the salinity of our corals bed systems (we have 2 seperate systems, one for sps one for lps and softies) and for checking our fresh batches of sw as we mix up the Royal Nature salt, 50g at a time. This tool makes checking the salinity much easier and faster and its definately more accurate.
The directions say that you should clean the lens with RO/DI water after each use and we do certainly recomend this.
Someone forgot to clean it once here and i went check the salinity and the Hanna meter told me the tank was 1.035. Obviously i knew this was incorrect so I cleaned the lens off, tested again and it was 1.025
Technically you are supposed to do this with all refracts, but mine usually just got a quick wipe off on a towel..... but that would also probably expain when my refracts need replacing every few years as they turn into a ball of oxidized aluminium
