As every liquid has a ph, and the ph pen is designed to test all forms of liquids for it's ph, I'm having a difficult time believing someone would dispute the pen and it's results. I have found mine rather accurate for both my coral (saltwater) aquarium and my growroom.

Perhaps you're refering to the soil probes which are, regardless of manufacturer, garbage. If not, I'd like to take a look at that Canna link. Mind posting it?