Hi,
I use a large "Lawn-Flite" strimmer, which has handlebars and harness, the machine is quite heavy but can be balanced well by moving the handlebars and carefull adjustment of the harness.

Iit originally came with a steel brushcutting blade, I have replaced this with a head which will take nylon stimming line. It is neither auto-feed or bump feed.The cutting head requires 6"-7" lengths of stimming line which are easily inserted into the head and held in place by special grippers. I buy bulk rolls of stimming line and it is available in round, star and square profiles and is available in different thicknesses from fine to about 1/8" diameter. I precut a couple of dozen lengths and when the line gets a bit ragged just push the old line through a thread the new line in, ejecting the old line in the process, this just takes seconds to do.

The new head cost just over £20, but its well worth it and economical to use, I believe auto-feeds can waste line and bump-feeds are prone to jamming. I can't remember the name of the manucfacturer, but will post details tomorrow ( its a bit late to go down to the shed now! plus the bogeyman might get me!!).

Jeff