Hi daisymay,
I`ve been using a petrol strimmer all weekend, after all I wrote about battery ones :-[
It was a real eye-opener, My allotment buddy lent it to me and he`s very skilled at neatly trimming grass and doing jobs I use my little battery jobbie for. I was a bit more erratic but I got the hang of it although my arms were tired afterwards as were my hips and back. You really need a face guard hat or goggles and ear-protectors with a petrol strimmer which will push the price up and good footwear and gloves. (theres another thread about this somewhere)
Its a bit fierce and I think I could destroy my planted-up allotment with a petrol strimmer. I had a Black and Decker rechargable for a while which I liked but the switch failed and I couldn`t turn it off, now I have a cheap Pro-craft 12V trimmer, the handle broke 5 mins out of the box and the company don`t answer my emails anymore. It runs for about twenty minutes and is just for doing the paths and lawn with.
Someone here posted about getting a petrol generator which will run mains tools of all kinds which are a lot cheaper and you get all the benefits of a petrol driver tool in that you get power and run-time. This seems like a good option.
Have fun whatever you buy, stay safe,
Keep you fingers and toes if you kept them `til today, Col
Edit: The other thread about petrol strimmers is in Basics