This style of game is fun, but it, like all the copies that came before, it is a rip off of another game. When a devs decides to "take inspiration" from another game, it should be because they want to change something they saw as a flaw. What Heroes vs Hordes does is not that.
Like all the other copies, the user in bombarded with micro transactions, and apparently the developers think their game being ad free is worth $20 USD... when they receive less than a 0.01 USD per ad from the advertisers; the game would have to show you significantly more than two-thousand ads to make $20 USD, did I pay for no ads, no, of course not, I'm not an idiot.
There is nothing wrong with supporting a game that you like, but there is something wrong with a game prompting the user to spend $2-$20, potentially more, on every screen, and in my experience from just an hour, multiple times per screen; I believe the most Xs I had to tap to close requests for USD after going to new screen was four.
Gone are the days that app developers make a game that they would want to play, now the game is intended to pull as much money from the user as possible before the user realizes that the more they spend to progress, the more the game asks from them.
If you haven't installed it yet, don't bother, there's better copies out there.