The Pinecil works really great. Have been using it for a while now. The non-linux products from pine64 are pretty good.

It's an excellent soldering iron, hardware wise. Lightweight, heats up extremely fast, holds up heat very well. Never tried a custom firmware, but had no need either.

The pinecil is very good.

Although the firmware mine came with had an issue and I did have to update it, I now prefer it to my Hakko.