The Jumbolon boards look like they should do the job you`re wanting to do.
There are some things to consider.
Is the roof the highest point? In other words, is there an elevated border, like a parapet, around the sides of the roof? If there is foam board might not be good because any water that gets between it and the roof will eventually make its way into your home. It may take a while, but over time the water will permeate the concrete if the concrete is unable to dry out as it does now when the sun comes out. If you use it in a recessed roof, you will need to caulk around the seams and edges to prevent water coming in. If you live where it is dry, you won`t have to worry about this and foam board will be the least expensive way I think. Also, foam board might not stand up to high winds, even if it is properly glued down to the roof.
Spray foam might be easy to put down if you have the right equipment but most of us don`t. If you are hiring someone to do this and they have spray equipment, then the spray foam is probably the best way. Just make sure your contractor knows you expect him to apply the foam so that it is of uniform thickness all the way across and that there are no large depressions area-wise in the application. This means if your roof is not perfectly flat that the foam will tend to make it flatter. To keep water from standing. Make sure the roof is as clean as you can get it. Spray foam won`t stick if there is a layer of dust or dirt on the roof. Also, if you are doing this make sure you get each pass of foam where it seals against the one before so the installation will have no seams. What you can do is get a piece of wood, spray some foam on it and see how wide it is when it sets up, then mark lines spaced that width across the roof so that you will have a reference line for each pass of spray foam. Try to spray it all when the temperature is relatively uniform. Say 11 A.M to 4 P.M. or some similar time window. You wouldn`t want to start spraying in morning when the temp is 40F and continue through the day as the temp rises to 80 or 90F. The foam will expand at different rates and to different dimensions.
I would extend the insulation at least the thickness of an exterior wall when measuring out the rooms so that you get some overlap to the roof you don`t want insulated.