What RC for my Nephew

[RZ1]

My nephew wants to get into RC, so wanting some advice.

I have been having a look and have shortlisted either the Ansmann Mad Rat or the Ansmann Macnum.
With either of these we will be looking at getting them in kit form and him building them up to learn a bit more about them.

What is the general feeling on these, are they any good for a 11 year old kid?
How easy are spares to get hold of?
How easy are they to upgrade in the future and make them quicker?
Is it possible to get car shells for these as opposed to a non descript shell? (thinking something like hummer shell etc)
Has to be an off roader as he is likely to use it in either the garden or the park, and maybe occasionally in a tarmac car park.

His budget is only £50 and i am going to buy him the extra bits, tx/rx, esc, battery and charger as a present. (If anyone has any of these bits they want to sell drop me a pm please.)

Any preference on which to go for?

Cheers