Hello, I tried the last beta in a MBP 13'' 2011 with 1TB 850 Evo and seems to work very well. I upgraded from a Sierra with FileVault, the full process included whatever it does to convert to APFS took around 1 hour (I was expecting it taking longer as I had around 900GB used), what I have not realized is on a relevant space gain but I might be wrong as I did not wrote the free space before the upgrade.
After the migration it was needed some time to convert messages database and reindex Spotlight database (I did it overnight), but after that it is clearly working better than before.