Just got the new shield pro 2019 (was using a loaner 2017 shield from a friend till now), and I absolutely love LOVE it!!
Everything just work seamlessly, no lag at all, the 2017 shield had microlag here and there. The new shield remote, which is built really well, has an IR emitter so it works with the AVR as well. power button on the shield turns on/off all three devices and shield input is automatically selected. The harmony 700 I just bought is useless now.
AI up scaling is decent, all my old hanna Barbera collection does look a little better. DD and DTS audio passthrough happening perfectly, barring the occasional need to reboot the tv cuz of shitty CEC implementation. DD TrueHD and DTS HD MA is not supported via ARC so that only happens if I plug in the shield directly to my aging AVR while loosing all HDR playback capability.
Also next to zero jank in plex (plex server on lan on a windows box while shield is on 802.11ac). Only time plex hangs sometimes is when rewinding aggressively.
I would highly recommend the 2019 shield pro if you have the budget, costs about 16k in the US right now. Prime sale starts tomorrow on Amazon US, so might get discounted further.