Why you should not: it's inferior to SQLAlchemy and has a dual licensing model where one is the useless AGPL and the other is an expensive commercial license.
Also I find it's implementation to be very questionable.
...expensive?! Maybe when you compare it to free. But for such a crucial piece of infrastructure, this looks like very cheap, IF its friendlyness is backed by SQLAlchemy-class code quality.
The fact that there exists good free software out there doesn't mean that one should adjust his price expectations based on this. Take Linux, it's free, but this doesn't mean it's development was not fueled by up to $100M worth of contributions, so if Linux it's free, this doesn't mean that a team developing a new OS by themselves should not charge a price big enough to quickly amass a tens-to-hundreds-of-millions-$ class profit to recoup their investments.
You give something fully for free IF and AFTER you've recovered the development cost, or after you go bankrupt or pivot to another product and you no longer have any use for it. If you do it before, you at least make damn sure nobody else can make a profit from/based-on your not-yet-paid work without giving you at least some of it, because this is how it's fair to be, this is what the (A)GPL is for!
As much as AGPL annoys me the pony developers seems to understand it and use it in a reasonable way.
What really annoys me is
1. when people stamp a AGPL license on something (that was previously licensed under GPL or even less restrictive) and claim that it is still just GPL and everyone could still continue using their system as before.
2. when people make something brilliant and only offer it under AGPL without providing a commercial licensing option.
3. when the code is AGPL, receives contributions, then the original author offers a commercial license including said contributions without any contributor agreement.
Also I find it's implementation to be very questionable.