I’ve had both cheap and expensive blu-rays, and they all looked the same on my Pioneer plasma TV. I expect you aren’t going to see any noticeable improvement in PQ until you get to the really high end players costing thousands.
As far as the apps of those two players, you can find that yourself in the manuactures’ web sites just as easily as I can.
On the settings for the BD-S681 you can turn off the 4K upscalling and select Auto or 1080 for your tv resolution and i believe the player will work fine for a non 4k tv.