I just bought a MZPlay but almost bought an S7 Edge, so I created a pro/con list for the Edge. Things that were helpful for this device, and I' assuming still apply to the S8 are:
Native inductive charging!, IP68 water/dust resistance, Gorilla Glass 4 on both sides, GPS includes both GLONASS & BDS, for added security–Samsung Pay + Knox, higher RAM, split-screen native, FM radio.
As for specific advantages for the camera itself:
Optical Image Stabilization, f/1.7, Dual Pixel = faster focus & reduced blur, LED flash, Auto HDR, Phase Detection Autofocus, larger sensor, can shoot in RAW, Pro mode (focal length & tone), double tap home button to activate camera
I really wanted to feel like I would never need to bring a separate camera for most photo situations. –I was just out of town for a week and took both my Moto X2 & Canon G7 for this reason.
But given all of this, battery life was crucial to me so I chose the ZPlay anyway. I was coming from a Moto X2 and the Moto Active Display was probably my favorite Moto-specific feature so the ZPlay also gives me this feature. As for the "only HD display," this wasn't even a factor for me. I've been pleased with the X2 display which is what the ZPlay has. I prefer that it sips less battery than a Quad display so, again, back to the battery feature for me.
On the minus side of the ZPlay is the lack of cases/accessories, etc., as compared to anything Samsung. My local Best Buy store told me that they've never carried cases for the ZPlay, "because the mods." What a moron.