A lot of work to stabilise my site..
I used these guys before Christmas. Just got my site back to normal this week. It was amazing how my site appeared faster with the results that they sent me. However, I was not able to replicate them on either GT Metrix or Pingdom. In addition to this, my site cache filled so rapidly that I had to clear it at least once a day and was getting warning emails from my hosting company! Finally, I also found that my site was becoming really unstable, and would often crash while I was administering it. I have now uninstalled everything they had done and reconfigured my plugins. Site is now nice and stable, cache is not filling up super fast and I've made the correct changes myself which means that now my pages are served at a good speed. Zippisite are very cheap, and there is a reason for this.. If you really care about your site, and it is image heavy I'd say AVOID. I've learned my lesson. They are polite people and try their best, but for me it was a disaster. (Although I have learned about optimising site speeds!)