Which one works well and can save me time and some effort?

I have tried the manual(100% human labor), but this , at the time did nothing, a spade or a large knife is better - but a ton of work, I must have a mile of edging to do !

I have seen a nice (I think) power edger at Ace Hardware for a little less than $300....and I have a Weed Eater parts machine ( auction - $1.00) missing many things.

Which machine will cut out garden areas in the lawn ? Or should I continue to do this by hand ? I love using good machinery when it works well.