Let me start by saying I own and have used Airmail, Airmail 2, and Airmail 3.
Aside from the fact that I've paid for them all and I've got subscription fatigue, this client offers nothing unique, so I can't see why I'd pay for it. So far you can't configure swipes, the actions from Airmail aren't there, etc. This really isn't a full client and it surely isn't worth more per year than Airmail 3 is perpetually. Also, there are free clients that are far better and this one struggles to set itself apart.
That said, it's far prettier than AM3 and "feels" more iOS-like, so I'm hopeful this evolves into something better. I had started using Edison Mall as my primary after getting crushed with the aging look and feel of v3.
It's a good start, bit more of a beta than a proper app. The free version is far too hobbled. I mean... no notifications?! I can't recommend this to anyone, paid or not, right now. But good luck to the team on evolving this!