I just activated Replain on my website. It's VERY EASY to implement!
For me this could be the most ingenious CHAT app ever and it has the potential to be revolutionary for small to medium businesses that want to be able to chat with their customers while keeping things simple.
In my opinion the strongest point for them is how easy it is to use this, even if you can use messenger you can use this, because guess what, YOU ARE USING MESSENGER. Due to this there is no need to train anyone or have anyone log into a specific software or app, they can just use what they already use on a daily basis.

Most likely everyone here at AppSumo are tech geeks who like to be ahead of the curve in terms of new apps and technology but most of our clients aren't like this and don't like having to learn new things and understand new concepts. This just works within their limited IT capabilities and there is no need to struggle and to expand their capabilities. To put it simply this is a REVOLUTIONARY approach to an OLD platform (messenger) allowing for new capabilities while keeping the same familiar interface.
I can easily see a hairdresser, or a car mechanic using this tool to easily to communicate and engage with their clients through their website/messenger/replain.

Where they do need to improve is in the UX, it desperately needs a re-design, maybe consider checking ENDORSAL with their easygoing and catchy design interface.

I look forward to this re-design and some awesome things that I saw on their roadmap!

Best of luck!