It is the best google to salesforce integration on the market. support is incredibly responsive and very helpful. They are constantly adding new features, and the current feature set is well beyond anything else that is currently offered in the market
If you are looking for a way to integrate google apps and salesforce, this is the single best tool available on the market. For the price at which it is being offered, it will pay for itself in just a few days. You will become more efficient using it, and that extra time saved will make you more profitable as well.
The plugin is installed inside your internet browser as an extension/add-on. It can be found in most add on stores and is easy to install. Usually just a few clicks. It handles authorization for you once you sign in, and then takes care of all the rest. It couldn't be easier to get working right out of the box. You're up in running in less than 5 minutes.
Very easy to use. Everything opens in a familiar interface right inside the google apps sidebar. It brings in salesforce records, so as long as you know google apps / gmail and salesforce you'll be all set.
Cirrus was very easy to work with whenever I needed help or support - which, thankfully, wasn't that often. They were available via email and chat. But, like I mentioned earlier, there wasn't much need for support...The product just works.