Herpstat is awesome. You can pay with a credit card on the spyderobotics site, its weird though. It still shows a paypal receipt, but only charges the credit card you provide. I know it sounds strange, but I have done it twice. You could just call them as well. The ND model is the way to go IMO even if you do not plan to do a night temp drop. It has many other cool features that you don't get with the regular herpstat.