Hi Cotton,
This would depend on the specifics of the bunkie board but any rigid non flexing support surface will feel the same as any other rigid non flexing surface surface. The only real difference between a firm non flexing slatted bunkie board and a firm non flexing foundation would be the height.
If a bunkie board has a solid surface and isn’t slatted then it would significantly reduce the airflow under the mattress which depending on the other risk factors involved can increase the risk of mold, mildew, and dust mites (see post #10 here). There is more about the different types of foundations that are generally suitable for different types of mattresses in the foundation post here and there is a little more about bunkie boards in post #4 here and in post #4 here.
As you probably know I think highly of Tom and Royal Bedding and they would certainly make a great quality/value choice. They are what I call “mattress people” 
Phoenix