The popular opinion of the modern mind is that firearm/edged weapon combos are silly affectations that those crazy old guys in olden times were kinda fond of.
In reality, they absolutely kick heavy amounts of butt, when kept in context. As Not2Sharp pointed out, the idea is to be able to give a single volley and then use the blade.
This has some significance in hunting, if you hunt like those crazy European nobles did(actualy, I do sometimes), but it's mostly a defence issue. On a utility knife, it's a bad idea.
I don't think these two knives are realy designed well to be functional pistol knives, in this case someone wanted to make something, but wasn't sure what it was supposed to do.
It's like building a car without taking into account how it will be driven. Nothing wrong with cars, just this one won't be well thought-out.
Like any other weapon, a pistolknife can be done poorly, but a well done example is a quite useful weapon, in context.
I built one in fifty caliber(blackpowder) some time ago from parts I bought at Dixie Gunworks. Not a kit, though they do sell one, mine was homebrew. It worked real good.
Balance wasn't adversly effected, it handled well, the extra weight didn't bother me at all because knives aren't heavy, and it was as accurate as I am for as far as I can shoot a regular pistol(not far, maybe 20feet, ranged weapons have never been my strong suit).
Since I suck with pistols, I like the idea of being able to give a volley before falling back on the blade. I keep meaning to make another one that fires modern metalic cartridges, something fat and slow like a .45 probably.
Now if you want to argue that they aren't as effective or accurate as modern firearms, I agree. If you want to say they aren't the way to go for a utility knife, I agree. But if you are saying they are inherently poor weapons, you are just, wrong.
In context they work great. Before reliable repeating arms were developed they were a good choice to give you the ranged attack of a firearm and still be able to instantly fall back on an edged weapon should it misfire/you can't reload. For those of us with limited abilities with pistols, they can be a good answer. For people who enjoy physical combat in the woods with wild animals, they are effective.
