I like that it is easy enough so anyone can use without needing any training or support - just go in there with your laptop/mobile phone etc! It's not as intuitive at other systems but if you're ok using drop down menus then this shouldn't be an issue either way (although we had some issues getting used too them).
We've been able to keep track very well since starting up our own small project management system which has helped us manage costs better than before by being more efficient when managing people hours spent working away during office times vs out site time e.g.