There's a difference between back-wired devices and back-stab devices.
Back-stab devices allow the wire to be inserted in a hole in the back where it is then held in place by a spring-loaded clip (which you can't see). The back-stab retention system is no longer permitted to be used in many applications, including on circuits over 15 amps due to high failure rates of that electrical connection.
Back wired devices, on the other hand, are preferred to looping the wire around the screw (sidewiring), as when the associated screw is tightened after a wired is inserted, a backing plate clamps the wire into place for a secure, reliable and low impedance connection (it's faster and, electrically, at least as good). Your GFCIs are undoubtedly back wired devices.

Do they still sell the backstab junk?

They're still out there, supposedly only with the back-stab holes too small to accept anything larger than a #14 wire.