Low Earth orbit debris isn't a long-term problem. Atmospheric drag is enough to bring things down before too long. At the ~600km altitude these satellites use, they might last a decade or two before deorbiting naturally. Possibly less, since smaller satellites have proportionally more drag.

Higher altitudes are a much bigger problem, since debris there can stay up for a very long time.

You're correct. In addition, it's important to note that conjunction (collision) risk is proportional to spacecraft cross-sectional area. Thus, even with 100 of these small 10cm x 30cm spacecraft, they still pose less debris risk than a single satellite with a few square meters of solar panels (of which there are plenty already in orbit).

I don't think that's quite right. Say for example a number of small satellites were arranged on the points of a triangular grid pattern, with the points the same distance apart as the diameter of the spacecraft: This would result in a much higher collision chance (for a spacecraft passing through) than if there was a single satellite with the same amount of cross sectional area.

Nice, I never considered the impact of cross-sectional area on the actual collision risk.

Actual footage of the 88 being released in orbit from another thread.

https://news.ycombinator.com/item?id=13653040

Planet is very careful about space junk. One of the founders even did work for NASA, v.v. space junk. All the doves will burn up after use

Well burnup or re-enter

But of course re-enterring with these materials is a burn