all very good points by out to lunge, only time you will need a bi metal blade is for cutting stainless steel lips, and then you would use a diemaster blade, stuff goes through stainless like butter, sent one i made up to fatfingers who was having probs cutting his lips out, and now he is problem free, as for tpi and types of blades, use neo or flex, for wood,and pay attention to what lunge said about blade thickness, for example the salt water guys love the 18 tpi 1/4 neo or flex blades for cutting the lip slots for there pikie or metal lip lures, nice clean and small lip slot every time,i use a 1/4 inch flex blade with a 4tpi or 6tpi, for cutting my pine and basswood lures, but will go to a 3/8 blade 4tpi for harder woods like maple, hope it helps,
Etch