the Grounding Probe does not assure you that your fish wont get fried. in fact it pretty much assures you that if you do have a leak, your fish will be 'tingled' until you figure out that you have a voltage leak, which will be longer as the probe may hide the tingling from you...
that is the 'pro v con' discussion that experts / electrical engineers have, which is way above my level of epertise..
i would strongly urge everyone that doesnt have a GFI or GFCI to go out and get one today... They can be found built into electrical cords and outlet strips.
the average cost is about $20
This will assure you that you wont DIE when you get electrical shock... or rather you wont get the electrical shock.
It will turn off everything that is plugge dinto it and you may suffer issues related to tank health, but yo uwont die...
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=18026Or anything, doesnt have to be from drsfostersmith
Most houses have a GFCI circuit already, and i fyou plug into that circuit, you are covered... (these circuits are usually started in a bathroom and may extend into the kitchen or patio)
And to be clear, I reccomend you get this WAY before yo uthink about a groundng probe... As in get this today!