A few of my buddies and I got the United when it came out and used it quite a bit. Ball is a lot more round than I think most expected, and wasn't all that great at opening up the lanes. I still have mine, but really only use it in practice as a ball I don't hate putting a lot of meaningless (in score at least) games on.
I'd agree that Motiv hasn't really hit the home run on the flippy balls, the Original Primal Rage was really good, but since then it's been hit or miss, the new Lethal Paranoia is a lot closer, but still doesn't zing like the Storm Pearls that every has come to love.
While not the main focus of this, the Trident Quest has been a complete home run in my area, it's the most popular pearl assym, and that's with a high volume pro shop run by an EBI staffer and and two other shops with no bias in the area. It's been pretty interesting to see die hard hammer and Utah guys give it a try and fall in love.