I have a 3/4 acre yard with some flower islands, some trim around the trees, etc, so weedwhacking is an imperative part of my yardwork.
I first tried a Toro cordless rechargeable weedwhacker. It sucked. Zero power.
As far as the pull-the-cord-around versions, I can relate a tale of woe about a similar yardwork device. I had a Black & Decker hedge trimmer that was electric.
I used to hate the job of trimming the hedge because unwinding, yanking, and winding back up 150' of extension cords was a complete pain in the @ss and it took so very long!!
Then I bought this Stihl weedwhacker and fly through the job. You can buy other heads to put on too. I trim my ~100' long hedge with an angle-adjustable hedge trimmer accessory thingy. It's such an obviously perfect tool that people frequently stop and ask about it.
Oh yeah. And I've had the thing for 3 years, never serviced it (just routine maintenance like clean & grease, sharpen the hedge trimmer blades) and it starts up reliably every time.
Now the yardwork is actually relatively fun if you can believe it because the tool is so perfect for the job(s).
Here's the hedgetrimming head. There are lots of other things available, from a limb-trimming chainsaw to a power broom. There are tons of varieties of hard cutter blades too.
That's my story. YMMV.
[edit]Oh yeah. Just be sure to wear earmuffs (and eyeglasses but you'd need that with an electric thing too) because this thing is L-O-U-D!!! But using it is like compressing time. I just did the hedge yesterday afternoon and had to rush before the rain came. Gave it its 'high & tight', cleaned up the clippings, ran back inside just before the downpour started. Sorry to go on and on, but my appreciation for that thing grows every time I use it. When I was choosing what to get, I read similar raves about the Echo ones as the Stihl and obviously from the posts above that comes across here too, so I hope I didn't sound too brand-specific.
[edit2] TedTheLed -- Yup! I use the hedge trimmer for brush clearing. Works great but (a) you need to be more careful near rocks & things than you might if you were using the less expensive sawblade attachment (b) after a summer of hard use whacking down saplings perhaps a little too aggressively sometimes, the blades will need resharpening.