I seriously wouldn't be without a probe in the kitchen, so much so, I have a couple just in case one decides not to work! Obviously I need one anyway to for other temperature checks, but it is invaluable for cake checking.
There are many ways to test if a cake is ready to come out of the oven....colour, no cake mix sticking to an inserted skewer, listening for the delicate 'crackle' subsiding, cake contracting away from the sides of the tin....but my favourite is using a digital probe!
Not only does it act as a skewer to test for raw cake mix, but it is the only true way of finding out the exact temperature at the centre of a cake!
When my cakes are near their cooking time, I give the top a light touch and check there is no wobble, make sure the cake springs back instead of creating a hole, and then insert the probe....a reading of 85˚C confirms that there is definitely no undercooked egg in there!
It also means that I know a cake hasn't been overcooked, in which case it may be drier and require different attention after baking.