Personally I would draw a comparison to this unit and one that I regularly use to give you some advice as you haven't received many responses to your thread.
5 Plague Marines with 2 plasma guns cost the same as 5 Command members and 2 plasma guns.
I've found my plague marine equivalent to be very effective firing out of the top of a rhino. I don't think you should give all members plasma, as that would give you no ablative wounds (apothecary, 4 plasmas, any casualty will really hurt you there). However giving the 2 non-plasma veterans flamers might be a decent idea.
This unit is indeed useful for popping transports and killing monstrous creatures, and is best used in a list with quite a few rhino transports/other vehicles. They really come in handy when you need to kill some terminators or other strong close combat unit.
The only thing I fear is that they may take away points from other parts of your list. If you don't want to invest a lot of points into a unit of sternguard, I think the command squad could be a fine alternative, but you should test it and see how it works.
My chaos lists are much different from space marines lists, however, so I can't really claim to have a lot of perspective here regarding how effective this choice will be.