PJ, how did you get in my attic? Seriously, That method used in the picture in my opinion is an abhorent way to install flex duct work. The Y branching method is fine if installed correctly. Is that amalgamation of ducts that I see installed correctly? NO! there is your answer. Is it going to be a problem? That is not a question anyone can answer except the technician who does an airflow analysis on that duct system. So tell your client to hire an HVAC professional to perform an airflow analysis. If that is not acceptable then you or anyone else cannot honestly answer if "It will be a problem".