And the winner is...
Wow, the thread on Flyer is getting longer by the minute. The prevailing view is that SD has brought out a good product and users are liking the way SD are receptive to user feedback. Not much said about the comparison with ANP save for general comments from some users who prefer SD. Having both, but still inexperienced with both, I find SD more intuitive to use and that's the one I'm going to invest time to learn properly.
Personally, I also like the idea of supporting a UK software developer which appears to be very user-orientated and willing, for example, to spend time following long forum threads and contributing.
There's a debate about price. If you own an iPad already, it's less of an issue. Relative to other costs of flying, the price doesn't seem unreasonable to me. SD need revenue to keep investing. That is in users' long term interest.
I'd be interested in a ground school which shows your how to make the most of SD because I suspect my learning curve will be inefficient if it is self-guided.