You forgot to read the notice on the package that says it is a replacement spout only for use on cans made before a certain date, I'm assuming in 2012 since I don't have it in front of me at the moment! Also, the instructions suggest using a stepper drill bit to get a more round hole for the air vent, which worked out pretty well.
The last go around with a 5 gallon gas can was when I went to top off a portable generator. The outside temperatures had warmed up since filling the can, so I loosened the spout to release the pressure. The thing still sprayed gasoline all over the generator like a fire hose! I had to pretty much remove the spout and actuate it by hand in order to release all the pressure it had trapped inside.
I'm not sure we have the same product. It mentions nothing about only on certain cans. Also, my instructions mention a stepper bit as one option OR a paddle bit for a perfect hole.
It's possible. I bought mine from a local chain store that shall remain nameless so as not to compete against your offer, but the labeling made it sound like it was actually illegal to install the spout on a newer fuel can that was originally equipped with an "anti-spill" spout.