Monolift
Pros:
Safety
you can have safety chains or bands to catch the weight
No walking with the weight so less chance of knee or hip injury
Easier to lift heavy weights as no energy leakage from walk out
Cons
You need another lifter to operate the lever
They cost a shit load of money
Its easier to lift the same weight as a walkout
Walkout
Pros:
Cheaper rig to buy
IPF requires walkout on all squats so "train like you compete"
Cons
Its harder. More energy required to get to the squat position
More chance of injury.