The main disadvantage of "german method" is when you want to flush the cartridge with water, from time to time
If you are flushing then maybe something else is at issue. I use the Durchstich method of refilling my CLI-8 cartridges and haven't flushed one in years. I am not a prolific printer like King
@jimbo123 either. My printer went dormant for 7 months once and all cartridges, still in the print head during storage, worked. I only use one set of cartridges, the other set and spares in dry dock for years.
For complete disclosure, a year after using my printer once again, the olf Magenta cartridge had flow issues. I replaced it with an old flushed, dry as a bone empty cartridge. It took a few days after filling for the ink to properly saturate the sponge, but it did without human interference.
Long ago I did flush some cartridges. Some were flushed without further modification and the flush water shot out the Durchstich hole and the manufacturer's air hole on the top of the cartridge. I have seen people use syringes to push-pull flush water in-out the cartridge but I never tried it.
Years ago I drilled or tapped a hole in the top of some of the cartridges - exactly what you would do for top filling - and flushed the cartridge . Yes, it seemed a bit easier overall, or maybe it took a little less time, but not so much as to require the top hole for flushing if you use the Durchstich method.
BTW, I still use a many year's old cartridge with a silicon plug on the top and another old one with hot glue gun sealed hole on top. The hot glue gun seal has remained patent for years. I suppose now that I've said that all Hades will break out.
Of course, in this particular matter it only matters what each of us thinks.