Using PTFE spray on rear derailleur springs
You most certainly can use a PTFE spray after cleaning, but, I would use a high quality chain lube instead.  

I use this dry teflon lube on my drivetrain and use a precision applicator to lube my derailleurs after I clean the drivetrain.

Personally, I wouldn't use any WD40 branded lubricant on my bike.  Also, I'd recommend not using a spray type applicator to apply lubricant on small parts.  I like to use the precision applicator, i.e. the long, skinny straw, to be able to reach into all the pivots of the derailleurs and accurately apply the lube.  The spray can be messy and will often contaminate other parts of your bike, like rotors or brake tracks on your wheels.

The 'Dry' lube is nice because it doesn't pick up that much road grime in the derailleurs.