Reading the info on a forum for the vehicle you are considering flat towing is a good idea.
Case in point, the Dinghy Tow Guide says you can flat tow a C-Max. That is a true statement. However...it can, and often does, drain the 12VDC battery! On the C-Max forum you'll find several folks who killed their batteries flat towing. The work around is to supply a 12VDC feed to the C-Max battery.
After finding out the "gotchas" I went with a tow dolly to avoid all the expense of a flat tow conversion, and the Ford warranty issues, associated with flat towing.
2017 Sunseeker GTS 2800 QSF
TOAD: 2016 Ford Edge Titanium FWD