Good idea, but not cheap compared to Aranet4 ~200USD. Not sure ESP32 is a good choice for power consumption.
What's a good alternative?
My understanding (which may be wrong, so I am open to being corrected) is that the greatest power consumption you'll see from ESP32 is connecting to a network and uploading data, the idea being less connections mean less power consumption. The ePaper display should be nice and low power consumption, too. I'd expect a common pocket battery bank to power it for a few weeks if one were using it to gather data for later use.
Again, happy to be corrected. It's really fortunate that this post showed up on HN since just last month, I ordered a few components to start making my own air quality sensors, the goal being to create some units that I can strap on my car and gather data while I travel for work (personal curiosity, mostly). There's tons of great projects and info being referenced in this thread.
OP is probably comparing the ESP32 to a NRF chip. These offer Bluetooth connectivity while running from a coin cell with <1mA power consumption, compared to the ESP32s ~50mA when not sleeping. Luckily, we can stay in deep sleep most of the time to save battery.
We mainly went with an ESP32 because of the great SDK and software support through Arduino etc. That way, people that want to customize the firmware or build their own can get started quickly.
It's a sensible choice. From a newbie perspective, it's certainly easy to work with and there's no shortage of documentation when I'm trying to figure something out. I'd pull the trigger on one of your devices right now because of that if funds weren't currently an issue (sadly, I am between jobs, atm).
We're always looking for beta testers and would be happy to send you a device. Find your contact details here: https://networkedartifacts.com/about