Strimmer heads

Our allotment association had 2 petrol strimmers ( a Honda 4-stroke and a Stihl 2-stroke) and an electric strimmer (Stihl) for use by members. I'm the committee member over-seeing machinery, and one of the major hassles is STRIMMER HEADS. Long ago I swore a deep oath never to have anything to do with threading my wife's sewing machines, but strimmer heads are worse!
The problems we find include - having to re-thread the cutting twine; bits breaking off the plastic head; loss of metal grommets that the thread emerges through; heads becoming so tight that we can't dismantle them.
We've tried various makes and designs of heads, but there have been issues of one kind or another with all of them.
Does anybody have any recommendations for particular makes or designs of strimmer heads to minimise problems?
(We find that the heads that fit our Stihl also fit our Honda, which is handy. The thread to attach to strimmer is sunk into the body - we have encountered designs that are completely different, and would never fit our strimmers).