IO-550 in the Legacy was having a horrible time LOP with the Champion RHB 32E.   I ended up testing the resistors, found them all failed, some in the 200k  ohm range.   I did a test using some of these surplus BG-341 (RHB32E equivalent) plugs and eventually went to a full dozen.  In flight LOP with a mag off resulted in complete smoothness.  It was like night and day.  Calls to Champion went nowhere.  These plugs have about 200 hours now, they cost me $9 each.  I have not yet tried Tempest but at this cost, I'm in no rush.  Champions would now be my last choice.