It would make Flashlight way too easy IMO. The reason it only has a 1.12x in the first place is BECAUSE of the memorization. It's not too bad for notes 1-199, but at 200+, it gets quite difficult. Now, if you knew where the notes where, especially on easier maps, no memorization would be required, hell, it'd be easier than hidden because you knew which direction the notes where, eliminating the main thing that made Flashlight mod-worthy in the first place!
Sorry, but I disagree with this mod idea, and it'd be really hard to balance if it was an add-on. It'd just make having Flashlight as a difficulty-increasing mod... pointless, because again, it'd take away the main thing that made flashlight so difficult in the first place (the other one being Lights Out, though that isn't too bad). No memorization required = way easier, and it'd be at least 1.06x, if not 1.03x. I think it'd be better to keep as is, off no add-on, ect.
Sure, it'd be harder to follow on harder songs, but easier songs? Psh, might as well ALWAYS use the Flashlight mod on those! I mean, if you didn't use the Flashlight + Radar on those by default, you'd be screwed, because it'd be a really easy bonus on those songs. ;(
I, however, would rather have the radar ALONE, as a mod that made it EASIER (and would reduce your score). It'd help newbies get into the game a little because it'd be slightly easier to see which way to go to get that note that is on the other side of the screen and you have three seconds to reach. =P Maybe have it be one of those quarter-circle wide ones that extended a bit, but went in the direction of the next beat? It would be quite easy to see that way, and would probably be around 0.70% score IMO.