I'm planning to purchase something in the game. Any suggestion?

Oh and job crystal vision card is great for farming in auto repeat or for job point quests

The monthly visore pack is pretty good, sometimes special deals in event shops (anniversary, version update, 2 million downloads, etc.) 2000 paid visore for 4x UR isn’t bad, relatively speaking, think that recently means 2 units 2 vision cards. The MR summon tickets were great deals, particularly with the UR gauge that filled up too and capacity for magicite or king or burst pots.

Also the daily purchase rewards are great when they include shards you need or items you need. Can buy the daily energy packs in shop for 99 cents to get credit. The purchase visore with 100% bonus free visore can also be good when you want to have regular visore for shards (don’t recommend for summoning as RNG is basically gambling, and they have guaranteed URs on occasion). Select UR vision or unit shards can also be good, particularly on hard or expensive to acquire shards (Gilgamesh and in the future Sterne knight of Ruin whose shards cost double a normal UR)

I've not made any in-app purchases so far. However I recommend you to spend money for summoning UR units you want, trading shards (fragments) of that units at the shop, and obtaining awakening materials (rainbow shards, starbow sphere) .

To unlock 2x speed battle, you have to reach Royal (vip) rank 8. You can also spend money for that goal.　

Don't spend your money for purchasing EXP cubes, getting metal slayer at the special shop, and obtaining ramada or macherie unit at the special shop. It will be waste of your money unfortunately.