Any "primary" CO2 regulator can be used as a secondary. What differentiates a "primary" from a "secondary" is the maximum inlet pressure it is rated for. A primary regulator is typically rated for 2500-3000psi. A regulator that is designated by the manufacture as secondary may only be able to take an inlet pressure of say 120psi. A primary does not have to have a high pressure gauge, and if you keep your CO2 tank inside the kegerator the high pressure gauge is next to useless anyway.
That said, since the pictured regulators do not seem to have a standard CO2 tank connection on them they are probably secondaries so you would have to feed them from the outlet of a primary regulator.