They may well be accurate, the honeywell switches I use are accurate enough although I always did index homing anyway. I could do that because my servo drives supported it but on the other machines that I have the CSMIO fitted then it does it so drives with homing capability are not needed.
Regarding an index homing board, there use to be such a thing, Ed Gilbert made various boards, one of which was just that. He doesnt make them any more as far as I know, in fact I dont think he makes anything now, his company was called CNC Building Blocks. I have a complete breakout board of his on the big lathe and it has the homing to index feature although I do not use that part of it now.
Hood