Ideally (IMO) you want your app to be recognisable - using plain material design feels bland - sort of like programmer art - as a user I'd gravitate towards a

Ideally (IMO) you want your app to be recognisable - using plain material design feels bland - sort of like programmer art - as a user I'd gravitate towards a more custom/tailored look - when done well it communicates effort and thought was put into something (at least to me).