
I really want to make this card work with Sefina Rousseau. I feel like Sefina's 4 Willpower is really not enough to use Mystic spells all that effectively, and her 5 health is obviously a problem. David could potentially kill two birds with one stone, while also providing a nice influx of resources. Jim would probably also be interested, as like Sefina he really needs Willpower boosts, and right now David is the only in-faction Ally who could provide that for him.
In practice, though, I've found David almost completely impossible to use. Obviously his benefits are not at all worth it if he costs the team one or more turns. And it's not like Arcane Initiate where you can just play it while the agenda is about to advance, the doom goes away, and that's that. This guy is no longer useful if the doom goes away. So unless there is a very long span until the agenda goes off, David doesn't work. That means that his ability is unusable the vast majority of the time in this game. I tried to use him over a number of different scenarios, and each time I drew him I either immediately saw that I couldn't play him and use him, or I did play him but ended up having to kill him off before I could benefit much from his abilities.
So right now I'd have to say this is a card that looks really effective at first glance, but in practice is just unmanageable. But maybe other people have figured out how to make better use of him.