Always had an interest in them - found the breed combo behind them to be interesting - but never saw any, or knew anyone here in the US who produced any.
Similarly, the RX3 cattle (composite developed by the Pioneer seedstock division, that was essentially 1/2 Red Angus, 1/4 Hereford, 1/4 Red Holstein) looked like they'd be pretty doggone good. There were still a fee RX3 breeders around the Midwest 15-20 years ago, but I've not seen anything about them in a long time.
I guess both ended up taking a backseat to the Simmentals, Gelbvieh, Chi, etc. - but it sure seemed like they brought something to the table; maybe it just wasn't enough...