Haven't used him this edition. While he's not complete garbage (at least all lords have T5/DR now), I don't think he's worth his points. In 8th you'd consider taking him as a cheap source of re-rolls for your daemon engines but none of those have CORE in 9th so why bother with a backline aura-giver these days? He's also not a whole lot cheaper than our other lord options and doesn't possess their utility. Might be worth a look if you're desperately trying to cram in a re-roll 1's aura or are playing a combat patrol but I'd rather try to find the room for another choice.
Silver lining (tabletop effectiveness aside) is that the basic lord gives us a lot more room for conversions than the other choices with their preset wargear. Real pity he can't take a manreaper though.
I have used him once. The dark Vengeance mini (painted as DG of course). I gave him the relic blade to make him more lethal. My opponent was very nice and allowed me to field him with a bolt pistol instead of a plasma pistol (when do you ever want a plasma pistol on a chaos lord ?).
I used him in a 1K army, gave him arch contaminator, and he was quite decent in that scenario alongside his Plague Marine bodyguards, running out of a rhino. He was probably not the reason why I won , but he was quite okay. A LoC would have been too expensive for my list, as well as the fact that I did not have that many units and wanted slightly more mobility, and he freed up enough points to give me 3 spawns instead of 2 etc. He also killed quite a few primaris around an objective. Note that I played a guy who wanted to field a thematic army more than a min maxed, so I did not go all out to make my list the most efficient it could have been points wise. I still won anyway as my friend is more a Lore-lover and a painter than a player (which is sad at some times, but on the other hand it also allows me to field some fun stuff that I wouldn't do against a "normal" opponent).
I do however think that there are not that many scenarios where I would consider taking him in 2k battles. Maybe, I haven't made that may 1K lists, he may be the cheap HQ you need in some scenarios I guess. But of course, normally, a Malignant Plaguecaster is needed. I think he is only useful in some 1K lists and combat patrols.