from experience if anyone has, would you go with d...

I like and have experience with gaia green and enjoy their line up. a lot of dry amendments are dusty and you will want to wear a mask when mixing into the top layer of soil. Both brands are very similar and I don't think you'd notice a big difference as long as the NPK ratios are in check. using both at the same time could be fine, just a waste of money I think if they are mostly the same ingredients. One note with gaia green I find it lacks in Magnesium and that will need to be added once a month. If you wanted some extra K as well it can be added in with their soluble seaweed extract. Good Luck!