The outside is waterproof, but the probe isn't. I've gone through two probes already, and i've traced it to moisture traveling down the cable to the joint between the cable and the hard steel part of the probe. I put a blob of high temp auto gasket maker silicone on the joint and it seems to be ok now. If you don't do this, I think you'll go through probes. I think they should use better probes.
Use shrink tubing. I've been doing it for a couple years now. I've had probes that have withstood accidental quick dips in the sink... I cut the tube about an inch long, slide it up the probe until the joint is in the middle, then hit it with a heat gun.