I use these all-brass drains for replacements of the plastic ones that seem to break all the time. The key to these drains is that compression from the brass ring that is used to compress the rubber seal does all the work. There should be no reason to worry about leaking if it is properly installed.
It will not hurt to use caulk in the area you mentioned if you feel it would help. The only thing I see that goes wrong with them is the putty on the flange. If the bottom of the unit was not set in mortar the bottom will flex and slowly break down the putty and cause a leak. No flexing in the bottom and putty can last for years without problems.