Earlier quoted context omitted.
To give it the fairest possible test I will take your concerns to an optimistic extreme. Given that I can set my thermostat back roughly part time, and most people work 40 hrs, and someone who can blow $300 on a thermostat probably works at least 60 hours, I will triple my theoretical savings to $36/year. Given a zero interest loan that would pay for itself in a "mere" nine years. Google products don't last nine year…
You act like products can only be purchased with a credit card. That is not in fact the case.
A reasonable opportunity cost might be 3%, I'm too lazy to bother figuring the time till profit because nine years at zero is already too long.