I used it occasionally. Thing is what I used it for was mild curiosity not really something I would pay anything for. Would rather see the features integrated into strava.
HAving the list of rides with the various data was interesting and an easier way to find things than going through strava by month. I haven’t really found a good way to search back through rides on there.
I liked the overall number as a measure of performance but I can live without it as it rarely changed.
I liked the way it gave you updated on positions in segments if people beat you or new ones were created.
There are various bits of interesting geekery on http://www.jonathanokeeffe.com
I use the heat map a bit.