They have a reputation for longevity.A few months ago I bought a Bluelab EC truncheon to replace the previous one which lasted 18yrs, from back when Bluelab was New Zealand Hydroponics.
I love it awesome for just stirring ya res to.One nice thing about the truncheon is it has the different conversions right on the pen. Most people refer to a PPM reading at 0.5 conversion from EC FYI.