Depending on how old they might not work for on ride photos that you can't tap after but otherwise for what you need; park entry, Genie+ tapping at rides if you buy it, tapping for photos or scanning for photopass photographers .... it should work fine and much easier than always pulling out your ticket.
If getting ride photos is very important to you, yes. Some are only available via MB. I have heard that the new Mobile Magic can also get ride photos but haven't tried it out for myself yet. I was there last month but due to knee surgery I was not riding much. I do use the phone for park entry.
If you really don't care about ride photos much, then you'd probably not really need it. Some (most) still have tap points.