It's only a bargain if the regular price elsewhere indeed is $23. But a google search learns you that this webshop in China is the only place where you can buy it, so that regular price is just fake. And so is the 5% coupon.

So it isn't a bargain. It's an alarm clock that costs $18.60. Only you can decide if you want to pay that amount for a gadget like that. If your son is a space enthousiast it might be a nice birthday present.