They are very responsive in terms security incidents that happen at my site as well has other clients I am responsible for.
Very easy process when it comes time resolving issues. Nothing really! If you have good relationship like trust between client/service provider this will not be an issue but if your relationships lack transparency there could always come problem down road (even though unlikely). The only thing would concern me about them was communication during incident resolution phase which can sometimes takes longer than expected especially after holidays season where things tend slow up due delays from remote employees being out sick etc..