Strimmer or Brushcutter it matters not. Buy something that comes with a harness and the big handles and is at least 5hp.This then gives you the option of using wire (for the garden) or a blade (for the waist high stuff). I tried the various combinations of wire,lollipop wire and the blade,and by far the easiest,and cheapest,was the blade. With wire,it took two men 3 hours to cut down 400 sq metres of grass. With a blade,it took me 8 hours to do an acre and that was taking it easy.All machines were Stihl and the same hp.
There are a few hire shops around so you could "try before you buy" and see which is the most comfortable to use and which one does the job best. Some retail outlets will even bring over a selection for you to try.......... Ree
PS Oh,and I made the mistake of thinking that the cut grass I left behind would be a good mulch to stop the weeds re-appearing. In reality,it inhibited the new growth of grass and allowed the weeds (nettles and thistles) to spring ahead. I wish I had run over the whole lot with a mower now and collected the cuttings. I now have a friends sheep (along with my 6 geese) on the paddock for a few weeks at a time to keep it all down and the land is improving quite considerably in quite a short space of time.