I think mail-in-a-box should recommend this software instead of current recommendation.
https://f-droid.org/repository/browse/?fdfilter=dav&fdid=at.bitfire.davdroid
Reasons:
- CardDav and CalDav are both supported and free.
- Its opensource and its free.
- It supports TLS 1.2
- It combines both apps into one.
- Its free.
- Its actively being updated and supported.
You have to install f-droid app to download from res. Really easy. Or download apk directly.
I have used this before and currently with owncloud .