Well I am sorry that the kendon stand up lift did not performing as you expected.
I have been using mine for 6 yrs now and have found it to be very reliable. After more than 100 lift's it has been problem free.
The olny problem I have had is getting the bike off the lift but that was solved when I built the 10 in stands (blocks) on each side to plant my feet on wile pulling the bikes off.
The problem that you are having with lowering the bike down is not a problem for me. Its a little jumpy like you said when twisting the knob to release the hyd jack but I have never had a bike "drop" on me ever.
One thing you can try is to not tighten the knob so tight in the first place. It don't take much to close the valve and not much to open it. Its very easy to stop if you keep your hand on the knob wile lowering it.
I find it harder to lower the bike and at the same time and keeping the air hose from getting pinched on the other side of the stand.
If you have one and dont want it maybe we can make a deal.
I know someone looking for one at a good price.
Best of luck to the bolth of you
2001 FLHTC Custom built 117ci runs well
2001 FXDXT (S&S SA 126ci motor) 136hp 137 tq w.625 cam.
2010 street glide..103ci 57 cams...fun and reliable...