I just use regular old starting fluid. Nothing fancy, just a shot in the intake.
The warning on the air cleaner is due to the automatic glow plugs. If the starting fluid hits a hot glow plug, it'll go off wherever the piston happens to be, possibly on multiple cylinders simultaneously, which is a great way to do a whole lot of engine damage. Since I have manual glow plugs, I just don't push the button, and it's fine. There are also those who think that starting fluid should never, ever, ever be used, regardless of glow plug functionality, for some reason. They are idiots who should be ignored on the issue.