I have yet to have an issue with working on either end. I do stuff on the website and I do stuff in FTM.
Hints in FTM got annoying, though, because in the mac product, you can't turn off hints for member trees like you can in the windows product, so I just turned off all hints in FTM.
I do, however, add info I find on other websites, add photos, etc. all through FTM while syncing changes made on the website from hints. I also like to review my place names and make them all uniform in FTM and then sync those up to the website.
The biggest issues seem to come with really large trees or people that have a lot of media. The tree I'm working on has only 1200-ish people and I have less than 500 media. So maybe if you have a huge tree it would be more worthwhile to pick one and sync to the other.
Anytime I've had conflicting information FTM always asks me to review/fix it before it continues with the sync.
I also sync a lot. I don't do a lot of work and then sync, I sync probably every 20-30 minutes. I figure the less changes it has to make at one time the less likely it will screw up....i hope lol
So long story short, its up to you the route you want to go as far as syncing one way or the other. I am using version 22.2.4.781 and I am on Yosemite 10.3. I haven't had hardly any problems at all. Keep copies of your backups just in case :)