It's barely worse phone, and it's a much better table. My argument for the tablet is that if it was a separate device I would basically never use it because it's inconvenient.
It has a smaller display with a crease[1] and has less battery than a tablet. The screen is even smaller than an iPad mini. IMO that form factor only really works for like a Kindle.
And the screen has a matte finish which is only going to reduce contrast.
[1] https://www.reddit.com/r/pics/comments/1wbx1wo/there_is_a_cr...
iPad mini battery life ~10-15 hours, iPhone duo 30+ hours so no...
Matte finishes are great for viewing outdoors too...