To say more, one would need to know CAA's pricing on the data they sell to MM.
AFIK the figure is zero. The aeronautical data is assembled at CAA DAP in Kingsway by the VFR Chart Editor who, as well as being a cartographer, is also a PPL. The previous Chart Editor was also a pilot, and has gone on to a career in commercial aviation.
I don't like it any more than you do but it is a fact that mapping data is jealously guarded by those who produce it and high fees are demanded for licensing it. A goodly chunk of the 15 quid you pay for a paper chart will also be going to OS because the CAA have to pay for it, just like MM. I've also looked at Memory Map but haven't been tempted. I suspect the attraction for most is that it uses the familiar CAA chart, making it easy to relate what you see on the GPS to the map, were it otherwise we'd all be happy with the mapping in our GPS's.
I suppose there's an opening for Jep there if they feel it worthwhile.
Sorry you thought me rude, please feel free to tell me I'm talking bollox when I do (it's a fairly frequent occurrence).
Mike