I've owned the HAL-O's in the past and currently use the UltraSonic's for the power tubes of my WA2. The HAL-O's are an easier fit because they're made of a flexible polymer and the actual dampers don't slide as much on the tubes since they're made out of a clear rubber material. The UltraSonic's are nice, but they can be difficult to install on bottle shaped tubes. The rings can be bent to reduce the tension, but the dampers are a harder material and tend to slide more.
I think they're definitely worth buying if you plan on tube rolling. I have a noisy pair of 6AS7G's and the dampers certainly help. I haven't tried them on the my preamp and rectifier tubes, but plan on doing so in the future.