For progression HoD will let you focus on mechanics more. Manually application sims slightly higher and gives you a gcd to move with. Once you have the fight hard wired I think it's best to switch to manual but HoD is never a bad choice...
I do feel like Demo (all lock) spec shouldn't be paying a shard for a cooldown. It is already throttled by cooldown duration. This will hurt destro a ton due to its shard slow down coming up. Our cool downs aren't that powerful to begin with.
Darkglare feels like he needs to be full time pet or compress his damage to be 4'ish seconds of burst AoE.
Speaking of AoE implosion needs a passive of the imps suicide automatically when they die. Keep the on use, maybe a small cooldown for the on use? (30 seconds and you get X shards) As it sits implosion is so weak and you just don't make shards fast enough to feed the implosion cycle....ID will beat it in practice.
Oh, and can demo get some resource recapture like shadowburn or UA+drain soul? I favor if something dies with doom on it you get a shard. Wouldn't change raid numbers much at all, but would be an amazing quality of life change.