PPM /EC pens are less likely to break unless dropped. I'm sure plenty of people will give you advice on which one to buy, but I have had good success with the
CAMWAY Digital TDS Tester Pen Portable Water Quality TDS EC Temperature Purity Meter Temp PPM Test Filter Kit 0-9990 ppm 4 Display Modes ppm, Μs/cm, °F, °C -Easy to See
Sorry, I just copied and pasted the text above from zon. It cost me under 17 CDN at the time.
Typically you can't go wrong with a PPM pen. Keep it clean and in a safe place and it should last you a long time.