greetings Holmes;
that's what i use, variable speed saber saw with a 17 tpi metal cutting blade. you are correct in thinking that the cut should be vertical as opposed to square with the surface of the deck. it makes the recess far easier to strip if you don't have to bevel the curved cut on the end of every piece.
i'm in the process of trying something different on the recess. i'm using 1 3/8 wide strips. i'm about half done the recess and it looks good so far. should be finished by next weekend. if it shows any problems i'll mention it on the board.
all the best;
daren......