Having seen gel tests, including some slow motion before the recent YouTube shenanigans, the Penetrators look good. Gel isn't the same as a living animal. Still, everything I know about physics and everything I can infer from shooting various media and random critters with different things tells me that these should perform well.
In terms of quality control concerns, Underwood is fairly reputable. I don't recall seeing any specific complaints. With Federal offered as one of the two comparisons, I've personally experienced a quality control issue with Federal American Eagle. Their customer service was spot on and they made it right. It can happen with any brand and I don't think these would be any worse.
As far as .357 Sig, I think this is a natural fit. The .357 Sig has a reputation for good penetration and that was one of its selling points. It does well against human threats with hollow-points and it should do well in the woods with the Xtreme Penetrators.