Let me clarify: Customer support is great. They respond quickly and try to solve problems. Issue here is plugin itself because is not exactly what it says.
PWA works great with some nifty features but has some bugs in accessibility (preloader, ajaxify at least). It states thegem theme compatibility but some theme functions gets broken with instantify (checked with activation and deactivation of instantify). I even made a pre-sales question asking for compatibility with my specific set of plugins/Theme and they answer that had no incompatibilities.
AMP is totally useless with a content builder (in these days almost all websites have one or another). You must have another AMP plugin to construct pages.
Instant Articles - Don't have an opinion. I have not used it so far.
Overall, there are free alternatives for each of the features that do the same. These plugin will be worth it when solves all those issues.