Depends on what phones they have.
Iphone 5 or upwards then i would say deffo stick the app on a phone.
Nokia 3210 - Tablet.
Anything with a tiny screen wouldn't be all that great.
I think the APP on a tablet is a bit overkill. Tried in on ipad air/ipad mini and just didn't like it.
I can see the appeal of a cheap tablet. For me as i am still on the tools. Clean house, put slip through door, pull phone out, mark off APP DONE! Really is that simple.
I purchased an iphone 6 plus and is now in a gorilla waterproof type case. Its the perfect combo for work and CP.
Large enough to use Browser CP/ Awesome for the APP and safe dropping it at work.