To put it short: It's a tactical RPG game with some text issues (the sole developer is obviously not from the States), but if you can get past that, you have a decent game with an easy-to-understand battle system.
There's not too much grinding required to finish the game; in fact, the game gives you 6 bonus dungeons per day to allow your extra opportunities to build up on currency. The game strangely runs on an energy/stamina-based system that online RPGs would have (both for your teammates and for general dungeon running), but when a teammate gains a level, their stamina is refreshed anyway. Plus, you also gain stamina potions per day, more than enough for your grinding needs (unless you're a hardcore grinder, but that behavior is not at all necessary until the latter half of the game).
There are IAP purchases to be had, but there is absolutely NOTHING in there that you cannot obtain in other ways. It's just there to speed things up should you not be patient. There is an Ad system and big table of rewards you can get for watching ads every 3 minutes (each ad is about 20-30 seconds); but you'll need at least a full hour and a half to complete the table. The reward table resets for a full 24 hours once you've nabbed all of the ad rewards.
I actually started a basic guide, but there are several things:
* I don't know where should I post it; there is no official wiki for this game, and I am not all that familiar with the board code here.
* The guide (in its current, incomplete form) has far too many characters to fit the contents in a single post
* The guide is STILL incomplete, as I said; I have not finished gathering data on every skill, character and individual stage strategy.
* Posting incomplete guides feels unprofessional (but that's just my opinion

* Posting it here (as opposed to the wiki-ish format I currently have for it) requires a lot of rewriting to account for the forum code
EDIT: I decided to edit and post the guide at Google Docs. It seemed a lot easier than attempting to edit it using the forum code here. It's still relatively "incomplete" but has the bare-bones information to help you all finish the game.
You can find the guide here at: https://docs.google.com/document/d/e/2P ... WjWnEe/pub