Devices to user for mobile app testing

We are small Dev shop who outsources mobile app development to a third party.  We do in-depth user acceptance testing of the app in house.  We currently have a couple an older iphone 6s and Samsung Galaxy S6.  Was looking to expand/upgrade our hardware.  Was wondering if anyone out there was using IOS and Android tablets to do their manual testing as opposed to smart phones to allow for a bigger display/ease of testing.