Slow if built on Ethereum, but the goal is to have this as a separate entity.
Now, I addressed this that it's much more than a messaging app. Messaging just happens to be a part of it. It's a communication suite and thus the offering is a product of security AND convenience; the latter is something predecessors have sacrificed.
It provides a mechanism to do payments to friends and this is a leap forward in how payments are done in Crypto, a completely secure data storage, ability to make absolutely private meetings, and to make announcements (even calendar based).
The problem has been that current messaging dApps copied existing services and placed it on the blockchain. Eso devs want to provide something tailored to privacy in all forms of communication, in one app.
I don't know. I guess I just don't see it how you do. It just doesn't make sense to me to build that on a blockchain. Messaging apps that arent built on a blockchain are already about as good as it gets. Most of them you can send payments from as well, or build a simple bot to handle it on slack, discord, rocketchat, etc.
Like I said, also with blockchains comes costs. Most messaging services are free. This is another big problem. How are you going to handle the transaction fees of every single message? Also, what about transaction/block times? Also, what about the security makes it better than centralized services?
I can't think of any real benefit to a messaging DApp. Or at least any benefit good enough for me to switch away from slack, discord, etc.
Payments: These will be Crypto tx; insteading of sending to a string of characters, you'll send to a persona of your friend. How is that not a great addition?
Security: The data is yours.
Tx Handling: Look at Steemit.