Disclaimer : I bought the Developer License 8 months ago, when they launched. I am French and I have met every member of their team at a WordCamp since.

I was previously using W3TC and I had to spend a lot of time tweaking each parameter to find the best combination for my websites. But not anymore, I spend now 10 minutes maximum tweaking minification, JS deferring, DNS prefetching... And the results are far better.

I haven't tried the CDN feature yet (it was released not so long ago) but my clients and I are willing to pay for the premium quality and support of the plugin !