I use cloudflare and it really works.

I use Cloudflare with A2 and I have seen a slight performance improvement. The biggest plus (I think) is that Cloudflare will block most of the spam bots that were visiting your site. I've seen my spam email/form submissions reduce dramatically. Another cool service that they do is when your site goes down, they serve a cached copy to visitors (with a message at the top) so your site is viewable even if your host is having issues. All free. Recommended.