Sluggish SSD performance and was running out of space.
Easy replacement; although, we added a challenge because we also had to replace the Lithium batteries (difficult) and both fans on this aging unit.
With respect to the SSD, we encountered one problem. The replacement SSD was a hair (almost literally) too big. Solution was to shave off a tad from the SSD itself.
Be methodical, double check your steps, and go slow. Having a second pair of eyes (and brains) helps to keep you on track.