Sorry if I sound irritated (I'm not), but the TL-WA750RE v2 is actually a great (if old) piece of hardware (with an unstable stock firmware).
Qualcomm's Atheros products are amongst the best choices for OpenWrt due to how receptive Qualcomm is to open-source development (Intel/Lantiq are better though in that regard though).
Realtek's WiFi drivers are horrid, so if you wish for an an example of horrid networking, there's that.
As for the TFTP method, I'm still trying to figure that out, not being experienced enough as it is, and my Linux distribution (Solus), not yet having TFTP server software (I'm going to ask for one soon).