First of all, we bought Avalanche a phpBB 3 premium theme.
The theme looked good until we discovered that all the buttons to modify a post, delete a post, report a post or quote a post disappeared and it was not possible to modify, delete or report a post.
With bulletin, we had an issue when we wanted to modify the color of different items that were originally apple green. There were a customizer to change the color and it downloaded a small CSS file to our computer. In the code of the theme, it was mentioned that we could upload a custom.css. So we pasted the code in the custom.css where it was mentioned in the code. Unfortunately, it didn’t work. Then, we added important to every CSS directives and it was a mess because we could not read the fonts anymore.
I have ended buying the Milk phpBB3 theme from themeforest which works well and give the opportunity to modify the theme without CSS.
Interestingly enough I have spent a total of $111 US dollars buying themes for phpBB which could have been equal to a Xenforo license in 2017.