I assumed these things were triac based, the ones I have used were. There are no "contacts" to burn. At that point there is really no advantage to a 2 pole device since they all leak some current. The voltage on the lamp (to ground) won't be full line voltage but it won't be zero either.
In the equipment I have worked on with solid state switching they don't even bother switching all legs on a l/l load. Single phase gets one device and 3p gets 2.
Triac switches don't really like 3 phase since there is no real "zero crossing" but they do work. Typically they use something several times the actual current.
