Having previously used another component for mail, I was blown away when I switched to AcyMailing several years ago. Everything this other component got wrong, AcyMailing got completely right.
It's user-friendly and powerful. I'm an Enterprise version customer and have had nothing but good experiences with the app and with the company. Their support forums are really useful when you get stumped trying to customize something.
I need to allow parents to RSVP for luncheons, and optionally buy lunches, I need parents to register for seminars, etc. DT Register is perfect for that.
I have had some parents have issues with other form tools on our Joomla site, but DT Register has been very solid.
Its only flaw is that it could use some improved layouts, and graphics, but in terms of functionality, it's great.
The only problem was that I could not get it to work reliably. It would not display the 2 calendars from Google that I needed to display on the site. The modules would work sometimes and then not work other times.
I paid the $50 for the paid support, but unfortunately, that was a waste of time, after the developer logged into the site, I received no feedback from him. Disappointing. Back to JCal for me.