With all due respect, it did overheat. I don't want to be argumentative, but it's not helpful-- or a good customer service practice-- to refute your customers' empirical observations. A unit that goes from fully operational, to marginally operational, to dead in three days' time obviously had a serious defect. You have to allow the possibility that I'm able to tell the difference between a device that runs hot and a device that's so hot that it's starting to emit smells, and which, by remarkable coincidence, ceases to work at all.
And you write "but as you've already returned it..." as if you're chiding me. Securifi sold me a product that had firmware problems, radio problems, some other catastrophic defect, and a peripheral sensor not ready to be used fully. I'm not being at all unreasonable by electing not to work with support to fix a defective unit, or choosing to try my luck elsewhere.
I'm one customer who had a poor experience. Neither of us wanted that outcome, but it happens. Your job is to apologize and thank me for my custom, not to contradict me and insinuate that I didn't care enough to work the problem with you. I'll note this in my Amazon review.
Again, good luck with the product.