Haven’t been about to play for months, sorry about that. 
The reason I put slow computer is because when I played Gmtower, it helped me when I didn’t have to go out of full screen mode and such. While I was making the comment, I was thinking of Gmtower not Tower Unite its self.
Anyway, that was just what I had to say. My bad. 
Given that the graphics options can be reduced so much that it looks like a DOOM mod, I’d say that if you found a way to run it with your iPhone 1st gen as a GPU it might still work.
tabbing out ruins emersion in games, game makers mostly prefer fullscreen so players get the best experience out of it