I had a chance to test out the FLIR ONE Pro Thermal Camera, which is a $399 mobile phone accessory. Just plug it into the USB port on your phone and you now have an infrared camera with the same resolution as the FLIR E6, which is my camera of choice. I reviewed FLIR's first mobile phone thermal camera, the FLIR ONE, back in August of 2014. Since then, they've come out with a few upgraded versions, but the ONE Pro provides a huge upgrade in image quality.
The Basics
There are three versions of the ONE Pro: iPhone, Android USB-C, and Android micro-USB. At the moment, only the first two are available. I tested out the USB-C camera with my Pixel phone. The nice thing about a USB-C connection is that you can't plug the cable in upside-down; it's the same up or down. The micro-USB version isn't available just yet, but FLIR says they'll start shipping this winter.
In the meantime, the USB-C version can be used with phones that require micro-USB, but you'll need an adapter that'll make the camera stick out from your phone. I have one of those adapters to connect my Seek Thermal CompactPRO camera to my phone, and it makes me a bit nervous. If you own a phone that uses micro-USB, my advice is to wait until winter for the right ONE Pro camera.
This camera has its own internal battery, presumably because it uses a lot of juice. It's nice that it won't sap the battery on your phone, but it's also one more device to remember to keep charged.
Setting up the camera was pretty painless; I charged the camera, installed the app, registered online, and I was ready to go.
Size
The ONE Pro camera is the same width as my phone, but it's almost twice as thick.

That's ok with me, however, because I use a case for my phone that makes the thickness about the same.
There's a big conspicuous dial on the ONE Pro that I first thought was a manual focus, but it actually adjusts the plug depth. See below.