1. I would only ask for RIS if I really needed it due to poor (but legal) VFR conditions.
2. In normal VFR conditions, I wouldn't be overly concerned at penetrating the Benson MATZ without advising them; I would, of course, remain clear of their 2000ft/ 2.5 mile ATZ.
Recently I was flying to White Waltham with a student and called for a MATZ penetration. Whilst in the MATZ, I asked for the London QNH as WW is under the LTMA - as indeed is Benson. Benson's reply to this request for information? "Remain on Benson QFE"....
Incidentally, I asked AOPA in Oct 2003 to investigate why Harwell's P106 still exists. Harwell is now a Business Park and the reactors were decommissioned 15 years ago. I'm still waiting for an answer!