if you'd like to know how well your lighting set up really is get a welders mask and watch the flow of plasma in the arc, it should be smooth .
You coil and core people should change out capacitor every two years or brightness is affected. But coil and core are very low thd and as already stated easily rebuilt.
After my experience with 5 brands of digital ballast I've decided there is only one. Where the first one I bought , a 1kw chinese made welthink worked like a champ it brought the cable guy to the door.
Lumatek , I do own one and it seems to work, don't have a welders mask to look at the arc so I just assume like all older lumatek it operates with a high percentage thd.
I'm running a quantum at the moment that I also have no comment on really, it's a ballast.
I bought a hydrofarm phantom that I THOUGHT was gonna be the shit but found out before 1 cycle was up that they do have defects, it was the first return the shop I bought at had seen of a phantom and they were surprised, I was def turned off by the phantom failure and went with solis tek, I won't be looking back.
Then there's the solis tek matrix I bought awhile back. I'll never buy another ballast .