In terms of supplyng them pre-filled do you mean each time or just the first time you buy 'em?
I have Mido holders and they are fiddly to load initially, one type more than the other, but I found them no more difficult to "learn" than darkslides. I tried them in a tent and that was quite frustrating and as for a bag I imagine that would be a nightmare. I am guessing that doing it this way was the issue.
I found that doing them in the open in a dark room made all the difference. There was a thread on here about NVGs that I asked a few questions on for this very activity, I find it is quite a tactile task, which I am quite happy with, but NVGs would make it a breeze I reckon.
I can maybe post some pics if people are interested to see a holder. It may take a few days as my PP digi thing recently passed on

Gari