I've been doing a little research on the Underwood Xtreme Defender, and it looks very impressive in ballistic gel. Is anyone using it, or have any experience with it?

https://m.youtube.com/watch?v=ClJcJ8LQFbQ

I've researched it too and am impressed enough to carry it.
The Lehigh bullet (Underwood buys them from Lehigh) is new and perhaps strange to many shooters and often state they're looking for a
proven street bullet. Without leaders there will be no followers.
There's a lot of calibers and different bullets that have caused perps to die. There is much about this ammo tested with ballistic gel and barriers that looks better than a lot of others to me. HP bullets are fine when they expand but the perment wound channel caused by these Lehigh bullets and Underwood loads them hotter than Lehigh loads theirs, as told to me by the Lehigh
rep himself.
Likely Lehigh's offering is fine too but I like what is often considered over penetration.
Again, I use it in my carry pistols.
Stay safe out there.
Poli Viejo

I've got some 357 SIG 65gr EDs on the way, that I'll be running through the chrono. It will be interesting to see how they do in my Glock 31C compensated barrel.

So I ran some of the Underwood 357 SIG 65gr Extreme Defenders through my Glock 31C compensated factory barrel. Here are the results from the chronograph.

2091 fps
2087 fps
2077 fps
2123 fps
2077 fps

The cases show no signs of pressure. The hole left in the target made the normal 9mm round nose look like 22s. The holes from the EDs are larger and sort of squared off looking.