... So it's pretty much clip deaths be-gone?
Not sure if that's broken or not 
Though the fact each bomb essentially transforms into... 4? extra lives probably/definitely is.
Oh, that might have been misleading. It clears bullets in a small circle after getting hit, but it doesn't do a full screen clear. You know when you die in Len'En? It's kind of the same, just with less invincibility frames.
It's not as great as it sounds. Plus Reisen is kind of meh as a shottype.
Eh, while I'm here I'll describe all the shottypes. Reimu is TD Reimu. Because the patterns in this game are so dense it can be hard to move around the screen. Her homing is extremely useful because of this. Her bomb is standard Fantasy Seal. As usual, her only "weakness" is that there are gimmicky shottypes that are better than her.
Marisa is DDC MarisaB, but with Master Spark for a bomb. The lasers are not piercing. She's strong and her focus shot does splash damage, but she has no range. Typical Marisa. And like I said, the patterns get really dense so Marisa will have a lot of trouble during stages.
Sanae's unfocused shot is like UFO SanaeB, her focused is like UFO SanaeA. Unfocused, she shoots slow moving frogs in a spread, and the frogs do splash damage. Focused, she has pseudo-homing. She fires snakes vertically. Once the snakes reach the height of an enemy, they move horizontally and hit that enemy. She can't hit enemies below her. (It's the same as UFO SanaeA). Her bomb is the same as UFO SanaeB's, the really long and really powerful one. I personally can't find any weaknesses with her.
Reisen's unfocused shot is a spread type. It's somewhat similar to MS Yuuka or IN Yuyuko- the individual bullets are strong, the spread covers a wide area, but you can't really shotgun with it. Her focused shot is a weak piercing type. Her bomb is like SA MarisaC or DDC SakuyaA, but it has no time limit and you can get hit up to four(?) times before the bomb ends. That said, it only clears a few bullets around Reisen and it gives very few invincibility frames so it's not as broken as it sounds. It's not noticable first but at full power Reisen will be doing much less damage than the other shottypes, and her bomb deals no damage at all.