I have been running the Onyx front and rear since 2002. Regreasing the body is a simple task, just take off the casette, loose the bolts on either side (with a normal tool [if your regard mm to be normal], no special thin wrench is needed or other special tools), then pull out the axle and pull off the body (be careful not to loose any roller in the inner body bearing).
After three years in wet service (some 2-300h each year) the body failed but spare parts ($12) and service was a small matter. Hurt my knee though. I got some photos at home if you're interested. Send me a PM if so, I might not check this thread again.
My only beef with them is that it has not that many engagement points, my riding has evolved quite a bit the last three years so they start to be an annoyance in technical terrain, where you track stand alot to regain balance and find the line over large rocks. Especially on climbs.
Other than that they're great! The seals hold up really well. Extremely well. Two thumbs up!
However, my next rear hub will have more engagement points. Hope to find something with the same quality, especially considering the sealings! My hubs take regular baths on my rides...
Oh, and the QR on the front hub is worn out. But hey! Three+ years! And I take off the wheels often.
And King, well, they ain't worth that much money unless you're into trials (not trails) - IMHO.