I like that it's easy to use, has many features in one place which makes managing multiple accounts easier than having them all spread out around different tools.
It also integrates with Google Analytics so you can see what keywords are working best for your site. There aren't any downsides as far as we've found yet - but there may be some things about certain aspects of the platform we haven't discovered yet! Make sure you know exactly how much time you have available before committing yourself since this isn't necessarily "set-it-and-forget" type software (like most services). We're able to track rankings better now and make tweaks faster because our data from previous years was scattered over various other platforms.