I do not have a Grand Kingdom.
I do have a Square Off Pro and Chessup1 (as well as others).
I would take a Chessup1 over the SOP any day of the week. Much better product.
There are other boards that are as good or better than the Chessup1 as well.
But for me, the SOP falls way down the list. YMMV.
I have to agree with Rsava, the Chessup is far superior to the SoP. I have several e-boards myself and if the boards you listed are your only choices get the Chessup. The Chessup is very stable and has rarely crashed on me. Also, the Chessup team have responded quickly and professionally to any inquiries I have made. I understand they are coming-out with a Chessup 2 but I am not sure if I will get that.
If you are open to other choices you might want to look at the Chessnut line. I have the Chessnut Evo and really like it.
To go with what @lasertswift says, if your options can be expanded, the Chessnut line is great. I have most of them.
The Air line is a smaller set, the Evo is the same size pieces but the unit is bigger, and the pro is a full sized set.
More money than the SOP for the Pro but a beautiful set to play on. The Evo combines so much in one unit, a great e-board setup.
which one is better: square off pro,square off grand kingdom set or chessup?