When I got my first BAII I was a teenager and didn't know much. I installed it on a MIM jazz bass and never did any grooving, just screwed it on (broke a screw in the bass too), strung it up and played it. Eventually the strings actually wore grooves into the saddles.
Surprisingly this didn't cause tuning issue or string breakage.
Don't have that bass anymore but since then I bought a Highway One Jazz which came with a BAII with grooved saddles.
I don't see why you would buy a non grooved one, I don't' understand why they ever made them non grooved in the first place.
I agree with Mtnman, no reason to make yourself more work, or give yourself the chance of screwing something up. Get the grooved. Also like Mtnman already said, prepare yourself, there seems to be a lot of hate of BAII's on these forums, not sure why?? I have no problem with the ones I had, and plenty of players use them.