Skulduggery Pleasant and Maleficent Seven - Spoilers?

[lucyanntrevelyan]

Question from my DS - he is reading the Skulduggery Pleasant series and has seen the Maleficent Seven is a spin off. He wants to know if he should finish the S.P series before reading the others because they might give away some of the series? Has anyone read both of these can let him know if there are any spoilers?
Thanks.

I read it after finishing the series but I think it's fine to read between books 8 and 9.
Book 10 has just been released.