I felt very good in the games I had with this very aggressive build. In mid / late game you can heal easily thanks to the life steal that you have accumulated with the passive and with the items. You will easily get 300/400 and more attack damage which means you will do massive damage and steal a few kills.
In addition, your R will reach a cooldown of less than 40 sec, and this already in the mid game! Definitely, with this build you can do enormous damage to your opponents and simultaneously support your partners with healings and shields.
The only defect: Senna is AD, and if the opponents bought items that give armor, they would resist both you and your ADC, so be careful!