We have a terrible sleeper. We have a baby hammock. It's made no bloody difference.
We got the hammock when DS was 2 months old. He slept in it for a few weeks, no difference for a while the his sleep got worse. I think his sleep patterns are entirely unrelated to wherever we lay his head. He's just a rubbish sleeper and there doesn't seem to be a cure I can put hase on eBay!
Not sure how helpful this is but I had DD in Miyo hammock from birth and she slept pretty well in it, if she startled she would set it bouncing which soothed her. Also if she was fussing I could poke my arm out of bed and bounce her to sleep. However she grew far too quickly and doesn't fit in it from 2.5 months, so we've had a rude awakening trying to get used to a cot bed with no bounce. It says baby can stay in the hammock until 6-9 months, only if they're very small! DD was about 16lbs when she outgrew it. It's supposed to see them through until they lose their startle reflex at 4-5 months?
we used the poco baby hammock and found it made a great difference, my little one is near to sleeping through now. I cant reccommend these enough if you looking for a hammock take a look for youself, not a bad price in comparison to some either i have no complaints on this one www.pocobabyhammocks.co.uk give it a go it worked for us :-)