I was wondering if anyone has used this stuff and if it is any good.
 

In short, YES, but it is called lots of different things all over the world, I use the same stuff but its called, 'friendly plastic' or 'polymorph' and is really quite a fun product to use, I have used it for so many different things I couldn't actually list them all here! but things that I mostly use it for is mechanisms, teeth for puppets, internal support for puppets, comfy handles for control rods and mechanism handles, etc.... the list goes on and on, but my suggestion is buy a small pack of it and experiment, it will inspire you and is a really useful things to have around. also as I'm sure you are aware, it can be coloured easily too, so is great for making things like animal noses, fingernails, hooves, etc..

Oh wow. I didn't even think of rod handles. Now how do you dye it? Just food coloring, RIT dye or something else?

LOL, I think once you try it, you will find so many uses for it! in regards to colouring it, there is actually a big range of powders especially made for adding colour to it, but they are effectively just powdered paint, I have tried one or two things to colour it with varied success, but the best is the stuff that's actually made for it, and you can find it on eBay and Amazon, you can even get a glow in the dark additive too which I have found quite helpful for making control rods where you will be operating the puppet behind a screen in relative darkness, as if you need to let go of the handles for a few moments, it a simple case of locating them again as they glow in the dark!! give this stuff a go, you wont be disappointed.