Works really well and simple to install. My site had started to be targeted by spam-bots with loads of the usual spam comments every day, and it was getting a hassle to keep deleting them from the Akismet spam file.
With this plugin installed, I get maybe one or two spam comments a week and these seem to be human-written ones, no automated spam any more.
Only slight issue I found was some unnecessary formatting of the 'tick to confirm you're human' box which was a bit of a pain to overwrite with css (see thread in forum), but not a huge issue.
Thanks guys :)