I've purchased (from this link) and installed a couple. I would say you need to be an advanced do-it-yourselfer to do it yourself. You have to cut a couple good sized holes in your airhandler and do some basic plumbing/electrical.
If you've ever installed a thermostat (including wiring it to furnace) you're ok on electrical.
If you've ever installed a icemaker line in a house that didn't have one you're ok on plumbing.
You need to be handy with tin snips and sheet metal to do the air handler work.
Here is the one I've installed: