Firstly, let me say that Jetpack is a fabulous tool for all blogs. From the way that it handles spam to security and load time, it's a lifesaver all over the place. With that said, if I had to choose something to nitpick about, it would be the way that it can sometimes take over parts of your website. It's usually small things, but it can set automatic picture sizes, or override style settings, which can cost hours in hunting for resolutions. One of our mantras with wordpress websites is "When it's broken, disable Jetpack first". It's just a piece of software that thinks it knows best, and while sometimes it does - it would still be nice if it just didn't default to being in control. That complaint aside, the hours it will save you in spam filtering, image resizing and site speed optimization are worth any angst it may cause from time to time.

I have been able to improve how I use my forms and advertising methods, measuring results from Jetpack. However, the greatest benefit has been the site security.

It helps us to boost our website's speed performance and for a free plugin, I would say- it isn't a bad option at all.

It is a consistent product with easy to understand metrics.

Overall, my experience has been generally good. However, other plugins perform better in particular areas - ie. for SEO, or contact forms. But of course, the benefit of Jetpack is it's all in one.