Yeah, I saw this but didn't know if it would work because he was using a different version of esxi (5.5). Wasn't sure if VMWare fixed this in version 6.5.

It doesn't matter, it's universal. There's no special setup required between ESXi 5.5 and 6.5. The steps in the article to use the VAAI plug-in you can skip if this is only for testing. You don't require VAAI integration to get NFS to "work".

Also, what would be the cheapest way to go for a NAS device that does NFS share more easily with esxi 6.5?

See above. I don't think this should be a concern. The QNAP device you have does NFS perfectly fine. If you just wanted to buy something different that's newer and maybe more capable, that's another story.