I buy it in spray cans by the case and keep a gallon or 2 for brush on applications.
Since I started using it a few years back, I no longer use WD40 or PB Blaster as it blows both of them away. I use Kroil when I need a penetrating oil.
As for the consistency, when it comes out of the aerosol can, it doesn't seem any different then PB blaster or similar. Main difference is it doesn't really dry (so don't spray it on your seat or steering wheel). In the gallon bucket size, it's a bit thicker then paint.
I use it everywhere. Spray on small areas, paint it on from the gallon for large areas.
Garage door wheels, hinges and chain.
Under mower deck.
Anything steel sitting outside.
Door hinges
Electrical connections.
...
Car manufacturers are starting to use it as OEM undercoating instead of the old tar stuff.
There's tons of uses as shown on their site.
I believe I do get it from Kellsportproducts (the link in Doc's post).