Ahh yes, my first 1CC on normal was Marisa B too. Eventually (and I mean before you become a pro, so don' think eventually is too far away), you get to a point where a bomb, no matter how puny it is...Ok, sa doesn't count. Err, no matter how puny it is, pretty much guarantees clearing whatever it is you bombed. At that point MarisaB will seem pretty pointless. You can do extra with MarisaB, and I honestly don't think it will be THAT much harder (mostly because her shot type isn't at half-power or whatever like ReimuA's or anything), but it is definately harder.
I found I spent more time perfecting the actual stage itself than beating Flandre though, so for awhile, MarisaB might be viable anyway until the stage gets to the point where you can do it without dying once consistently.