Buy in person from a garden centre where you can test the weight. Bear in mind that the battery packs for cordless electrical items can be heavy.
Or get someone in to cut your hedges down to waist/hip height and then you only need to use shears.

Thank you urbanite about hedge trimmer advice very helpfully as for cutting to waist height i need to have them around seven feet due to being next to a school playing also i love the privacy they give will have alook at long handled pruners in case any thick branches

I have just bought a Mountfield cordless strimmer which can also have a hedge trimmer option and am very pleased with it. I wouldn't go to a garden center as I find that their products are very lightweight models and not up to much really hard use. If you can find a business that specialises in mowers, chainsaws strimmers etc in your area their products will be a little more expensive but will last much longer and the staff will be much more knowledgeable about them.

Thanks for yor reply think i will spend a bit more and buy a better product rather than a cheaper one suppose only get what you pay for and it will get used couple of times a year savana12