I did use biodegradable BB's after the first batch of plastic ones. I shot about 2500 biodegradable BB's before I switched to IR. In my high, dry environment (8000 feet above sea level overlooking a desert) those biodegradable BB's take about 5 or 6 years to degrade. They were starting to pile up.
I liked the ballistic nature of the BB's, it's more of a challenge to hit a target with Airsoft than it is with IR, but it seemed like I would soon have them everywhere, so I switched. Airsoft is fun. I admit that.