We recently got rid of prerender because of the promise from the last article from google saying the same thing [1]. It didn't work.
1: http://googlewebmastercentral.blogspot.com/2014/05/understan...
[1] This image is from 2014, when Google previously announced they were crawling JavaScript websites, showing our customer's switch to an AngularJS app in September. Google basically stopped crawling their website when Google was required to execute the JavaScript. Once that customer implemented Prerender.io in October, everything went back to normal.
Another customer recently (June 2015) did a test for their housing website. They tested the use of Prerender.io on a portion of their site against Google rendering the JS of another portion of their site. Here are the results they sent to me:
Suburb A was prerendered and Google asked for 4,827 page impressions over 9 days Suburb B was not prerendered and Google asked for 188 page impressions over 9 days
We've actually talked to Google some about this issue to see if they could improve their crawl speed for JavaScript websites since we believe it's a good thing for Google to be able to crawl JavaScript websites correctly, but it looks like any website with a large number of pages still needs to be sceptical about getting all of their pages into Google's index correctly.
1: https://s3.amazonaws.com/prerender-static/gwt_crawl_stats.pn...
What were the page render times for the two types of page?
Historically Google has been using some fork of Chrome 10 when indexing. I'm unsure what impact that is having on the reliability of app rendering, but I also trust the Google search team has done reasonable checks ensuring common sites and frameworks render correctly.
I strongly suggest using a sitemap for JS rendered sites, based on my own experience.
Then again, I really like react+redux+koa (r3k) for client-server rendering.... Hoping to do something more serious with it in the next few months at work.