They are o.k. as long as they do not cost a fortune and they are not like a dingbats (or what ever it is called) question.
I have one on the Elise, as said it hides the age and is shorter so looks better.
Thought about getting my 4 year old son one for when he is older (they will cost a ££££'s by then) but there again he will prob not be able to afford to drive by then (we wll be priced out of being able to drive by then
)