Well it's certainly all I'm going to recommend, that's for sure. Your insurance adviser might agree... there will be no UL mark* on your home-grown solution.
You'll be doing just as much of the programming side of it by buying that device, and not lose out on any of that learning, and will have significantly less risk.
And yes, your safety first thinking and the post is spot-on.
Edit..... * not that I can see one on the pic in that link either... you might want to check its certifications.
More edit.... It says this on the instruction sheet:
Our liability is limited to the purchase price of this product only. By using this
product you agree that PowerSwitchTail.com, LLC can not be held liable for any
damages or injuries resulting from use or repairs