A great read+great magazine.
TL;DR: Old bikes last way longer than new bikes. From a production standpoint, steel bikes have a smaller carbon footprint than aluminum or carbon frame bikes. Conventional bikes use fewer consumables over their usable life than electric bikes. Among electric bikes, cargo bikes use the most resources to run and maintain.
My cousin, who works at a bike shop says that those things are super dangerous and break easily. Is this true in your experience?
Iirc the biggest reason they can be dangerous is that the dropouts (where the rear wheel mounts) were never designed to stand up to the torque of a hub motor. You can brace it with extra metal or stick with a low wattage motor and make them pretty safe.
https://www.ebikeschool.com/torque-arm-need-one/