Wind is the underrated factor
Outdoors, wind acts on large, lightweight slabs like a sail. A slab that holds securely indoors can tip outdoors. In strong wind, do not work with large slabs overhead, and secure the load.
Substrate
Concrete slabs, gravel and sand require different setups. A suction lifter only adheres to the top surface of the slab, not to the substrate. Check beforehand that the slab is clean and dry.
For natural stone in outdoor areas, moisture can weaken the vacuum. Dry the surface before lifting.
Outdoor tools
Verdict
Working outdoors requires more margin and more care. Plan the lifting path, secure the slab and, when it is windy, work in pairs if possible.
This guide is editorial and general. For safety questions the manufacturer datasheet applies.