Ground probes are a fancy sounding tool to poke into your gravel and substrate. I personally perfer to use a finger. We talking about the same product here? It's a little pointy widget to stir your substrate, check for pockets of anerobic bacteria, and debris? You need one if you don't want to get your hand wet, have fish that will eat you, or have such a large tank you can't reach the back corners ever.
WHAT????
all electronic devices throw off stray electricity...a ground probe in your tank will take that stray electricity, and direct it into your houses grounding system...it's a saftey tool...do you really need it ???...not sure, but you don't many new homes built with lightning rods either