Mobility BYOD security

Hi all. We’re looking to do BYOD within the finance sector, iOS and Android.
. Requirements are still being gathered but we’re thinking a stand alone email app. Would you enforce a security MTD app and if we do we’d have to change our view and enrol the device (not stand alone) so that we could enforce the mandatory install of an security app ( for mitm/certificate trust etc). Any views in either of these etc from our security gurus out there. Thanks