Well, I didn't say it's useless, but I've wired single receptacles into double or triple gang boxes like this for ages, and I think the prewired stuff is a little over the top. And I didn't look, but in most cases the severely raised price isn't justified. In simple words, most such stuff I've seen is DIY "make up", and way too expensive for what it actually is.
And remember, these things are backstabbed, so the procedure goes: Cut wire, one cut with strip pliers, and push into the terminal. Finished. Less work than pushing the device into the box, centering it, leveling it and tightening the claw screws.
