I have 3 computers, all HPs. As I drag application windows around the remote computer monitor in seamless display mode, a mess of rectangles the same size as the window is left all over the remote monitor and don't go away.  When I drag the app window back to one of the main computer monitors, one or more copies of the window I just moved is left on the remote monitor where it was original displayed.  Other than the left over artifacts, the seamless display works, well, seamlessly.  I can maximize windows, type into them as expected and so on.  

When I have mouse trails enabled on the primary computer, when seamless display is turned on, the mouse trails also leave lots of mouse trails on the remote display as well.  Disabling mouse trails stops that, but I use mouse trails so I can find the mouse easier across all the displays.

The refresh rate on both monitors on the 2nd computer before I turn on seamless displays  are set ti 60hz.  After I start seamless display, those same monitors on the main computer show a refresh rate of 120hz with no option to change them back to 60hz.

Lastly, when I disconnect the seamless displays, it takes upwards of a minute or so for the original displays to revert back to the control of that remote computer.