Cost effective is the bottom of the line isn't it?
Sometimes yes sometimes no, minimising disruption to 80year old nuns has no price.
When mixing wired and wireless the EMS would require another panel(?) to control the wired equipment (especially addressable devices) where as a Kentec Synchro for example can be used for addressable, non addressable and wireless all by a single control panel, easier for end user and maintainer both.
Each jobs different and chosing the right blend of equipment is the key to making it work correctly
By the way we didnt use Gardiners on this project we used a more competative local supplier who not only arranged the training and assisted with the site survey test equipement, they also provided the hardware ready to allow a straight out of box on to wall solution, simplifies the works on site no end, not sure on the rules for recommending suppliers so please PM for details if you in the South East/London area.