It is if you can't reach the release.
Still isn't, as you have to lower or raise the gun to properly grasp the slide.
You can release the slide with your off hand, as part oft he mag exchange cycle. (I've learned to do it for competition, on those guns that don't have "friendly" slide stops.)
What you try to do is keep the gun up near your face, between you and the target, so that you don't really have to look away too far.
Slamming the mag home and moving your off-hand on up, and using all of your finger tips to find the release and depress can be very fast -- and foolproof. After hitting the release with the "claw" made of your fingertips, the hand then drops down and you use your normal two-handed grip.
On the slingshot method:
One of the pro shooters I've talked with [he was an instructor in some of our IDPA group's classes] is now working with Special Ops guys at Fort Bragg.
He says they do NOT train combat troops to use the slingshot method any more, as they find they're having problems with the guns not going properly into battery. He advocates using the slide stop/slide release.