The Platinum international cartridge adapter has caused flow problems for some people. I've never used it, so I'm not one of them.
Platinum and Pilot cartridges are very easy to refill, and do not require a syringe. A disposable pipette (not the only vendor) is sufficient for either brand. You do have to pull out the sealing disk from Pilot cartridges before refilling them. There are youtube videos on resealing Pilot cartridges.
None of your mentioned pens are firehoses, so topping the cart up every so often (say, daily before leaving the house), should keep you from running out -- unless you're writing 8 or more pages a day.
Edited by Arkanabar, 14 December 2017 - 15:03.