Maybe once or twice a game. While my first reason not to have this was that their cost would likely go up, the second reason is exactly the quote above. 6+ does nothing substantial.
I like the idea behind the forgeworld ironsides. While the engineer guy (falk?) is with them they re-roll 1's to hit. They also have heavy armor for only 2 more points apiece.
And that's with a unit that is there to get into combat, and hang around a while. So for crossbowmen and handgunners, how often does anyone expect some light armour to make any difference to the game?
Even if it was given to them for free, would it make them any more effective on the field?
The way I see it, these guys are there to whittle down the core enemy targets, then once the melee is joined and they've got no target left they can assault the flanks of enemy units to disrupt, if you're in a pinch.
They could probably be a point cheaper, as part of an overall adjustment to the book that lowered troop values and increased war machine values. Or they could have upgrade options like the forgeworld dude, but then you need to either control unit sizes or accept you're building the ruleset towards really big units.