I'm 65 years old, so looking for 'payback' or break-even isn't something I think about very much.
(Since you can't take it with you)..
When I ordered my Mini-split after much reading and actually seeing the
cooling-only unit at a work site. I read the install manual, check out
the cooling (it was summer) and decided to take a chance.
Heating my home with the Sanyo is an experiment that worked out.
If it dies tomorrow, I'll be looking to replace it ASAP. (But with the latest design).