I'm not in any way a tech SEO, or a big publisher, but this one (at Tier 3 for me) is a keeper. As someone writing daily, and running a small but growing site.
My experience with support was excellent; Boyd @Nozzle went the extra mile to ensure I got set up. Good ethics = good team = good for us.
Having an enterprise-level rank tracker for life is a great deal, once you crunch the cost of monthly subs elsewhere.
The presentation of the results is very clear, and I like the way one can drill down into a particular keyword to see the exact screen capture of the SERP - from which I can learn. A great way to improve my own articles, and understand competitors.
It brings instant clarity on some issues: I thought I had slipped on one ranking from #3 to #4: a glance at the side-by-side screengrabs showed that a new PAA section was responsible (and not a new competitor).
I can definitely see that as this (already mature) app grows that it will continue to add value to my business. They clearly have an active development plan in place.