What should I consider / know about before replacing with a Stab Lok GFCI breaker?
Don't go there

The Stab-Lok GFCI-breaker is a two-pole half-width Stab-Lok, mechanically speaking, with one of the handles removed and one of the poles connected mechanically to the GFCI trip solenoid instead of having a normal trip mechanism.  This is a problem because it renders them quite vulnerable to the infamous Stab-Lok common-trip jam defect -- either an overcurrent trip or a GFCI trip could cause the breaker to jam up, utterly defeating its utility as a protection device.

Instead, fitting a GFCI-receptacle at the first receptacle on the circuit, or cutting into the homerun and adding a box for a deadfront-type GFCI, would be recommended, if you are not replacing the panel, that is.

(Note that new-build Canadian Stab-Loks may or may not be any better than their crappy USA counterparts, still are vulnerable to bus burnups, and are not listed for use in the USA anyway, so don't make the trip across the border either.)