I'd never heard of Let's Encrypt. It may be an option, but I see they won't support wildcard domains until Jan 2018.
Oh, and they're only valid for 90 days... hey, but it's free!
I'll have to research it a bit more, but if they're like self-signed certificates they are not really secure (no chain of trust established with them) because they are user generated. (Anyone can generate them--making them insecure, unless you trust the site in the first place--which makes it kinda pointless if you do already).
Best bet, and this applies with any web site, use different passwords, un-check "keep me logged in" on public devices, regularly scan your device for viruses and spyware.
Anyway, thanks for the lead!