Just received one
It did a 2p reinvest? I can’t wait! One more month until I get my next 1p 
It gets invested when you invest. As it says “your free cash will be invested as well”
I believe it also reinvests when it reaches a certain threshold, but that would probably be the same amount as the minimum deposit into the pie.
I mean that happens anyway if you have cash lying around in the pie and make a deposit into it