I have used a finger joint bit and feel it is certainly a worthwhile purchase. Setup is not hard as long as you don't cut corners with setup. You can't eyeball it, you have to push some test pieces through that are exact thickness and cut as final product. As long as you actual use proper test pieces you will be happy.
My suggestions are of course to not make the whole cut in one pass, choose bit with shallower and wider fingers.
As an alternative, if the goal is strength of joint and not appearance than there are other simple options. I like dowels for end-joining pieces with small end surface. For edge-joining of long flat pieces that's a lot of cutting for such a complex router but, biscuits and dowels are both easy. I also like using a strip of 1/8 ply or hardboard as a full length insert. Cut a saw kerf with 1/8" blade along full length of both joint faces then cut a strip of 1/8" board just narrower than twice that depth and glue it in the kerf. It keeps the pieces aligned and adds a little strength. Kerf doesn't have to be centered, just make sure matching sides are against table saw fence (top of both pieces against fence or bottom of both pieces against fence).
Good luck.
Last suggesting I could make with the finger joint bit is to glue it up right away. I've seen some woods, mostly softer woods actual have their fingers swell or warp slightly by end of same day to point where they don't want to match up completely. Probably due to high heat or humidity but still something to be aware of.
