1. Markup is broken. At least on Chromium. Everything is messed up. Icons for fields is messed up with text.
2. No standard way to change placeholder values for fields.
3. No way to add captcha (sometimes it is useful)

And here I thought ANYTHING would be better than the contact form that comes with Concrete5. Well, I'll give the developer an extra star for effort. At least they tried putting something on the market. But from what I can tell you have no options for what questions you can ask the user and doesn't have captcha. If you need a very very basic straight forward, easy to use contact form, this is a good one. But then again, the one that comes with Concrete5 does that. If you want any flexibility at all, this form is not for you.