I wouldn't ever buy any combi-instrument. Because EC-meters are robust and last many years, while PH-meters are sensitive need good care (actually the probe gets screwed up easily) and generally lasts only 1-2 years.
Do not buy any "TDS-meter", but an EC-meter instead. Actually everybody should go for EC and mS/cm instead of multiple ppm conversion rates, that in fact aren't actual PPM at all- and often lead to misconception of ppm, confusion and error!
Both instruments exist in resolutions of 1 or 2 decimals, as in .0 and .00. Lower resolution 0.1 is OK (and cheaper) to actually
measure nutrient solution and PH accurately enough, but to really
monitor daily changes, one decimal isn't good enough. Just because daily changes mostly happen in ranges of as little as 2 decimals. Hence with a low resolution instrument, daily variations/changes can't even be detected.