moldable plastic for device prototypes

[kunst]

I did not even know such a thing exists, I was told by a colleague about this thing. Moldable plastic is a product that can be modelled by hand and they claim it is non-toxic. I think it could be very useful for making a prototype of a device in order to be sure that the measure will fit before buying an expensive one. What do you think?
Just google for it...
EDIT:
I changed the original title of the post since I found that there are several trademarks for this: plastimorph, instamorph, plastimake....

[gilesenglish]

I've used polymorph plastic. You don't get much precision. Worth a go though.