I'll start off with the negative: Big problem for me is that I don't get notifications through my app when a new message is posted. This has huge consequences and should never happen!
Now on to the positive. I like this app, it has saved me from a daily load of horrible text messages by my X. He is now holding back in his ugliness, and when he does send me nasty messages, it is recorded and unalterable. The complete communication is one click printable and useable in court, as opposed to printing out separate emails and text messages. So it costs some money, I think the convenience offered and time saved is definitely worth a few bucks a month.
I would add wording in a court document that states communication should be about children's logistics only, this way there really is no room for anything else, making it (almost) impossible for narcissist to spew their gall. All in all this is a great tool to keep nasty X-es at bay yet still be able to communicate about your children.