I finally bit the bullet and bought a bottle of Citra from HopMyBeer.com
Honestly I am really impressed.
It has an intense fresh hop aroma straight out of the bottle. It's definitely different from hop shots (which is a hop extract), and way better than the water-based hop oil from hop tech.
1~2 drops will add an nice fresh hop aroma to most beers, but it does take about 4 drops for the fresh hop note to really come through in DF 90min IPA. I really love the fresh hop aroma, and it's actually way nicer/stronger than SN Hop Hunter. (I actually added it to that beer!)
I am yet to brew a batch with it, but I think I will add it straight into the bottle when I bottle it from the keg with my beer gun. (will probably only do half the batch so I can have a comparison.)
As for head retention, I followed their instruction to add the drop before pouring beer, and it has a beautiful head. When I add it over beer, the oil drop does seem to collapse some foam, but not killing the head completely. I think if I add it into the bottles, even if it separates out, it should mix again well when I pour it (similar to their instruction).
Overall I would recommend checking them out! They do have more stuff on their website.