The Ultrahubs have normal pawl mechanism, while the Hyperhubs have machanism like DT star ratchet hubs, Chris King, and the lightest rear hubs, the Tune Dezibels. Looking at DT's and Chris King's track record, the Hyperhubs should be more reliable and hopefully durable. The Hyperhubs are still new, so they are still under observation. The good thing is that Extralite hubs are very easy to maintain especially the Ultrahubs (just need the right-sized hex wrenches, 5mm and 10mm if I remember correctly), since I haven't opened the new Hyperhubs yet, but the manual shows they can be serviced easily too. You can even change cassettes by just removing the cassette with the freewheel (if you have spares) just before a race. grease them before a race and clean them after if you want, but dirt won't get in with the o-ring seals. I remove the o-rings when the weather is dry during a race for even lesser drag so I check them after the race when I get home. The Tune Dezibel is difficult to maintain and the preload mechanism is by using thin washers, unlike the hyperhubs that have easily adjustable preload. The Dezibels also don't have spare parts yet nor any instruction manual for maintenance because it is supposedly not out in the market yet. Well, that's what the Tune guys said when I asked them, but I went ahead and opened mine for curiosity. Was gonna change the bearings with hybrid ones, but the bearings were very smooth rolling and were as light as hybrids except for one bearing near inside the hub that is in line with the magnets. I changed that, but the difference was only one gram
Now the set weighs 910grams or 926grams with yellow tape and modified AC valves.
Anyway, you just need to protect your alu freewheels with flattened steel staple inserts if you're using cassettes without carriers. There should be a thread here somewhere about that.