All of the brands work pretty much the same way. Apparently there was an Israeli company where the owning family members had a spat and each opened their own company with a version of the basic design. Not sure how the patent process worked.

I do know that my Dolphin Dynamic worked great for 3 or 4 years then stopped working and the company gave me a TERRIBLE time about repairing it, sending it back "repaired" but not working twice, sending me raw lead slabs to tape to the handle for extra weight (As if I'm putting raw lead in my swimming pool water where my kids swim!). They finally sent me a replacement that worked OK but never better than OK. I ended up selling it to a buddy for $500, with full disclosure. He had no trouble with it.

Disgusted, I bit the bullet and bought a BD. When I had troubles with it after 3 years, I waited too long to get it to them and bought another (from LL) and that one ran a half-dozen times and failed. So I brought it to them, and, it turned out the old one was still under warranty, and they fixed both and had them back to me in days--the newer one was on my doorstep less than 48 hours later and has been fine since. The older one was a couple of days longer--and it's fine, too. No hassle.