Hi J,
I ran the Hydra back in the day. To be honest I didn't get on with it. I found them hard to fill correctly with the oil/grease. I also found them hard to seal also as they have a tiny black o-ring. I didn't like the feel of the Hydra on the track.
Thats just me, but I know people who did like them though. It just wasn't me. I was quicker with the standard slipper.
The club me and my parents ran was also on a farm which was bumpy,muddy and full of sheep, which occasionally ran on to the track............
I also think as well that the hydra may not stand the power of brushless, but I maybe totally wrong............