I don't want to sound off-hand, but - what are you worried about?

The application is basically a thin layer in front of AWS's Route 53. All user data is stored safely and securely.

Are you just as suspicious of popular applications that sprang up from hackdays?

I use to use DynDNS to access my POS terminal at my retail store. Dynamic dns is frequently an important tool so, yes, I would be very wary of using a hackaday production of it.