My final word on this (I hope):
FollowMee didn't work for me two days ago because, I found out, the data connection on my phone was turned off. Don't ask, don't ask. I won't repeat the name one of my sons called me.
Tested it today on a bus trip to physiotherapy at the hospital, all up and running BUT....
The tracking interval is 30 minutes. Apparently this is limited by the Windows Phone platform, which doesn't allow the app to wake up more frequently than this interval.
Therefore the track shows my five minutes walk to the bus stop as one straight line, and then shows a track directly to the hospital, ignoring the fact that I went via Harrow bus station where the next bus appeared as I got off the first one. Similarly the journey home shows me going straight to the police station. There's a bus stop there, honest guv.
Obviously results should be a little bit better on a 3 to 3.5 days walk, but as has already been pointed out in this thread, the app is dependant on a wifi connection, which I'm probably not going to have in the mountains.
Worth it? Hmmm, when I get a better phone, but then I'll probably be able to get a better app too.