it had some issues
"Offers 8 hours of warmth"? Maybe technically. The batteries have 3 settings. The lowest setting is barely detectable. The middle setting worked for 6 hours. The highest setting, the only one that kept my feet warm, worked for 4. Admittedly, my feet get colder than a lot of people's.
One of the two provided batteries would not go into Lock Mode, which prevents accidental changing of settings. Not a huge deal but it may have had something to do with the next issue. After some back-and-forth emails with Therm-ic customer service, they kindly sent out a third battery.
The Bluetooth app for iOS was buggy and worthless. It intermittently detected one battery and never detected the other.
In short, glitchy and borderline useful to me. I returned them and will now try low-tech Costco toe warmers.