Actually, it isn't better than wirenuts. That plug most likely isn't rated for the voltage of the ballast. If it stays like thay for a while, the prongs might weld themselves to the female end.

This isn't exactly up to code...however the plug IS rated for the voltage...it's rated 600 volt

Yes there are other better ways to do this though....

Best way I see to do this is to use those orange fluorescent fixture disconnects. I'm using them on my M400A1 FCO and have had no problems with it.

You guys know I changed this right? Now the ballast box has a terminal board from my busted traffic light and I used two lamp wires and the M-400 R2 socket and connected the wires to the screw on the terminal board, and have the wires from the ballast connected via slip on connector straight on the terminal block. I have a pic of it.

A terminal block sounds better.

I have used fluorescent (ballast disconnects) they are awesome!