Well, they mentioned enough details about the current 802.11r limits here: http://forum.mikrotik.com/t/v7-4beta-testing-is-released/158543/1
Of course your client has to know about 802.11r too 
And here’s a nice article: https://help.keenetic.com/hc/en-us/articles/360000862539-Wi-Fi-seamless-roaming