I've just played the first mission. It is playable but it's not stable (depending on the number of enemies on the screen).
I got Bullet Girls Phantasia today for PS4 and Vita. It's not cross-save, so that was a waste, lol. If you're going to get this game, get the PS4 version- it has a super-stable framerate and more enemies on-screen, plus looks super-clean, although graphically it's certainly nothing impressive. Tried Vita briefly and it seemed plenty playable to me on the first training stage, but those framerate drops...ouch. I hesitate to think what the Vita version is like on some of the later stages on harder difficulty settings-- might be unplayable.
Also could be possible that they release a day-one patch that helps performance issues on Vita- the game is not technically out yet. But if I weren't a collector, I'd be selling the Vita version off ASAP and would just stick with PS4.
As for the game itself, I wrote up some impressions elsewhere, but it's OK enough so far. They removed the ability to cling to walls/hide behind objects, but it doesn't seem as necessary since enemies are generally more melee-oriented. The difficulty is weird- normal, which is basically easy mode, is too easy on regular stages from what I've played, but the two harder difficulties are too hard, with increased numbers of enemy waves and they take much longer to kill. I did one stage on normal in about five minutes that took maybe 20+ minutes on hard to get to the boss on (who killed me immediately). The game seems pretty grindy since you'll want to replay levels to level up and get loot/materials to upgrade the characters and weapons. The harder difficulties also offer rare item drops that normal does not have. And yes, it's perverted as hell and has no chance of getting released outside of Asia.