Unlike other coupon offers that have been discussed on this forum, this one looks a worthwhile one. The places they have are a good selection of grade A attractions you really might want to go to, and places I take my own visitors to. The offer is actually run by the railway network in Britain, so they're really trying to get people to travel by train to London as well, unlike than the coupon-only companies.

Don't forget when considering where to go in London that admission to the major state museums like the V&A or the National Gallery is free, all paid by me the UK taxpayer.