Worked, not thrilled with performance - Real Avid Smart-Fit AR15 Vise Block

I bought this Vise block because other real Avid products were of good quality and innovative. What I found with this Vise block was a product that didn't work well. Fit into an AR15 lower was too tight, even at loosest setting. It didn't hold the lower upside down firmly...wouldn't fit. Seemed to break in a bit over time so I will keep using it, but not thrilled with this tool.