I think this is decent. - Real Avid Smart-Fit AR15 Vise Block

I was looking for one of the metal ones that I saw on a gunsmith channel, but it was overpriced. I do a lot of building, so I figured I would give this a try, as it's an upgrade to my old blocks. It does hold the receiver firm once tightened down. However, the angle of the magazine well shelf will not fit any of my lowers flush. It's not a big deal, just somewhat annoying. My lowers also sit at a slight cant when this is being utilized, which is still better than having them wobble around on one of the old blocks that don't tighten/expand. I wouldn't recommend using this to stake you castle nut though. Although it has flaws, I would recommend this product. Especially when it's on sale. I've never used the little red thing that comes with it.