The main problem with intarsia (from the gluing perspective) is that it is very hard to get a good fit when you try to get three pieces glued at once where they all overlap. Normally you glue two together and then re-lap the end of the joint(s) where the next piece must fit. It can be done the other way, but it takes a lot of time to cut, compare, and re-fit until all joints a correct. (If you over cut slightly then you have to throw out the short piece and start again.)
Look at the image below ...
In the first case (1) you have to cut both of the yellow side pieces to fit while maintaining the fit to the center piece. Now you can calculate the angles needed and take your time and lap them precisely. But I think you will find this is very time consuming.
In the second example (2) you only have to glue two straight lines with a little overlap. (You could also do the third side (3rd) at the same time (I just didn't illustrate it.) Once the glue is dried you simply use a trim saw to cut off the extra and then lap the sides flat again. Now glue on the other three side with a little hang-over, let them dry and again trim and lap the outside. (6 sides only two gluing steps) NO weird angles to cut.
Turns out even sided stones 4, 6, 8, etc. (if large enough) can be glued, trimmed and re-lapped in only two steps. Odd sided stone must have one additional step. 3 sided (3 steps), 5 sided (3 steps), 7 sided (3 steps) etc. (see small gray diagrams inserted in larger one.) They show the order of gluing steps.