Lock and load Alfred! There are advocates of both on here so sure you will get plenty of experienced views. I only know what I have read about vaping so speak with zero personal experience to date.
For me .. differences are cost and safety. Costs= Trickle is small amount of oxalic and a plastic syringe. Vape = vape kit, battery and most important, appropriate and adequate respirator.
Safety - trickle negligible safety issues used sensibly vape with no respirator potentially serious consequences.
Efficacy = reportedly better with vape, but some report individual hives requiring repeat dosages which is interesting. Trickle, possibly lower efficacy but still seems adequate in my experience.
For me a minor but significant issue is all my entrances are small and built in so many sublimators would have to be used under the mesh floor and possibly less targeted as a result.
For those with lots of hives all significant cost purchases becomes cheaper per hive.
Regards your final point - only reason I can think is that to register anything as a medicine costs a load but you can be sure that what you get is suitable for the use you are intending it for. Same as anything “Food Grade” I suppose.
If you buy pure honey, you can expect to get pure honey, not sugar syrup, for random example