Installed this for a customer.
Lots of messages didn't go through plus on many computers the captcha field did not show, which made the form useless.
Lots of financial damage done.
Really can't recommend it at this stage.
I gave it a 2 star just to be nice. Tried on 2 sites, and in each case, the form will not submit at all with this field added. Delete the field, and it works fine.
Yes... It does prevent bots, since it prevents the form from working.