Why would I choose a vertical PDU instead of a standard extension strip?

A vertical PDU is useful when you want a larger number of sockets spread along a long, rigid enclosure and would prefer the unit to stay neatly in position.

That makes it particularly handy under desks, on workbenches and in equipment areas where an ordinary extension strip can become a rather ungainly bundle of sockets, plugs and surplus cable.

It is still a basic indoor power-distribution unit rather than a managed or metered device; the advantage is mainly the form factor and the way it can be installed.