I recently developed a small WP site for a local non-profit, and decided to give CF7 a spin, as they didn't need anything elaborate to receive email from the public. I wanted to add a CAPTCHA or reCAPTCHA feature for added security to the form (it does not come standard with this plugin; you have to add it by extension with an additional plugin).
The CF7 CAPTCHA extension written by this plugin's author (Real Simple CAPTCHA) required some manual configuration of both the PHP engine (ensuring a GD image library loaded with PHP was activated), and checking or modifying some code in the CF7 plugin folder. Despite the promise of adding a CAPTCHA to CF7 as being 'real simple', that approach seemed too complicated for me.
Others have developed reCAPTCHA extensions of CF7 that generate a short code for pasting into a CF7 form. The reCAPTCHA plugin I used also required obtaining a public and private key from Google in order to activate the reCAPTCHA image (not difficult to obtain). Unfortunately, after activating the reCAPTCHA plugin, and pasting the shortcode into CF7, the reCAPTCHA image didn't show up on my contact page in development. The image DID appear when the site went into production. Then the reCAPTCHA extension hung up CF7 on the live site. Too much bother to troubleshoot.
So I turned off the reCAPTCHA extensions, and ran CF7 alone. I sent a test email from the live site to my Gmail account, but never received the email. I think the problem may be that my host (Dream Host) does not allow PHP to send email without a return-path email address set to the host's domain url (for example, setting return-path to: 'firstname.lastname@example.org'). The ability to set a return-path email is not available at the backend of the CF7 plugin. Nuts!
So I went back to using the Fast Secure Contact Form plugin, which I've used before. It takes a little longer to configure, but it's well documented and worked right the first time. Too bad for CF7. I really wanted to use it, but it just didn't deliver for me.