I am using an APU3 with the optional edge connector PCI-E with an TV tuner for my HTPC. Made a custom case.
APU2 for my Blue Cherry Security DVR. Stock case.
APU2 with pfSense behind my cable router. Stock case.
I have an APU1 for GPIO with external lugs for GPIO breakout. Made a custom rugged case.
The Intel 211 adapters are strong. CPU is weak but for battery usage it is ideal. Lots of expansion via Mini PCIe slots and mSATA.
Plus you can actually use feeebsd-update on them. Supported GPIO pins are a bonus.
They really are an nice all around utility box if you can live with headless.
On my HTPC I am using a 32GB Half Slim SATA drive for the OS and 256GB mSATA for TV capture.
The accessories are so cheap that I recommend all them from PCEngines shop.
The SD card they sell is quality for 7 only bucks.
I was thinking of making a APU chassis piggyback battery pack.
The 4"x4" size would allow a good amount of 18650 batteries with one layer. Somewhere around 16.
That would run the APU for a good while.