PH meters

hello forum,

i have gone thru a lot of cheap ph meters.
now i am looking at the inexpensive detachable ph probe
with small circuit for arduino style connection.
was wondering if these work as replacement for more expensive meters also.
was also wondering why the two styles.
it seems the blue ones have a replaceable liquid solution inside?
what is that solution and how often does it need to be refilled or replaced?

thanks.

If super accuracy isn't an issue it's much cheaper to get PH Indicator Test Strips.

My last pH meter slipped into a water container and was screwed after.