Android/Google Store review
The game itself is fun & addicting, however it's P2W (pay to win), even from a single player standpoint... It's going to take a TON of grinding & waiting (seeing as it uses a stamina system) if you don't intend on paying into the game. Microtransactions are what gives players an edge in this game & what holds back those not willing to pay them... Furthermore it appears the developer has made it a point to cut off players from the special events once they have been determined as free-riders in the game, so if you don't pay into the game for an extended amount of time, you'll eventually get cut off from those events.
The first thing I noticed when something was off was that the Next Competitive Stage notice disappeared & I didn't see the ability to play it. I ended up getting a Rankings are being calculated notice before I even got a chance to run that stage...
The second thing I noticed was the majority events were missing from my Notice tab; according to this list (which I found when I did a search online early this morning to try & verify my suspicion), I should have had access to at least 9 different events on the Notice tab, but this is all I had as of 1/16/2016:
Furthermore, this is all I had on my Special stage list:
So long story short, while it's stated you don't have to pay into the game to play it, they aren't going to ignore the fact that you aren't paying into the game & you will eventually be penalized in one way or another, so it might be better to avoid the game if you don't intend on paying into this P2W game (bordering on pay to proceed if they penalize you for not paying into it), as it will be a lot of wasted time in one way or another...
UPDATE: As of 1/28/2017 (a few days after noticing I was cut out of another ranked event, of which I didn't even get notification of it happening, but did get a notice of ranks being tallied), I have removed the game from my phone & don't expect I will be going back to it seeing as I will be started over again if I do (this also means I will no longer be recommending the game to anybody)...