1. MAINTENANCE SCHEDULE IS ALMOST EVERYDAY
When it first launched, there were plenty of bugs here and there. It's as if I'm playing the beta version of this game. Freeze screen during battle boss/battle duel, error while binding account (I will explain about this later if you have trouble on binding your acc because of region lock) and trouble on receiving rewards after battle. At first, they didn't tell us from their Twitter account for scheduled maintenance. It's just, boom, happened in the middle of the game before they posting something about it, resulting on several people complaining about how lack their communication with their player. Later on, after several angry replies, they finally gave announcement before doing scheduled maintenance
2. It's hard to stay F2P in this game
Every 10 gacha costs 3000 Rare Metal while sparking costs 90.000 Rare Metal (around 300 times of gacha in single banner). They gave us good starter tho, you could choose one SSR, one Pilot and one Scene Card as new player. And they also gave you free SR Orga+Mika+Barb as miling stone campaign gifts. But later on, it's really really difficult to collects RM. Daily mission gave you only 50 RM, main quest story gave you around >30 if you could accomplish their requirement each missions. Of course you could still collect some on event but it's hard too. I didn't really recommend it if you're temperamental with this type of gacha game.
3. Ridiculous Evolution requirement materials
Of course you could have easy resource from Atra because she sells items for upgrading+evol in certain time for 1 hour. But when you almost reached 7 evol or more, it required you to have it's own fragments. For example, Mika SR on level 61 required you to have their 75 fragments of Mika SR too to break the levels, means that you had to get him in gacha again
4. Binding Account problem
At first, I have trouble to do this because they said I can't register due to region locks. But I figured out the problem tho. When you registered your Bandai Namco ID, after filling email and confirming passwords, choose Asia-Japan region and do not fill it with your original region.