It seems that the SBS kit has suddenly come down £100, is it because they are trying to off load them now. It will not pick up ATC only the signal from the s-mode transponder which is a location device for ATC to pin point aircraft. S mode is used by all aircraft on airways but it is not required by GA aircraft until at least 2008.
By the way the SBS kit is like a VHF receiver in as much as it only picks up signals line of sight so if you live in a valley then you will only pick signals in the emmidiate area.
Good luck