HardHatAdmin has been very easy to use - it's so intuitive that I don't find myself asking questions or struggling with anything! Even better is that there are regular training sessions where you can get one-to-one help if needed which makes using this system even more enjoyable than other systems we've tried in the past (we're not really computer people!).
There were some issues around customising our own invoice templates but these have now been sorted out by the team at HardHat Admin who came back after seeing my post about them here on G+ and got straight down to sorting things out. We would definitely recommend giving Hard Hat admin a go as it helped us streamline invoicing & billing processes across multiple sites without having to spend time going through each site manually every week/month etc. It also means less errors being made when sending files via email.