We have a Sleepyhead for DS2. Same as you - they weren't around when DS1 was born.
It's bloody brilliant IMO. DS2 settled in it really well from day one. He napped in it as a newborn and looked very cute and cosy in it. At night, he slept in it on the bed next to me, which was great because I could just reach over when I needed to feed him and pop him back in when I was done, without the safety worries of full-on co-sleeping.
At about six weeks we put it in the cot and he sleeps beautifully in it. He's gigantic (in 6-9 months clothes already at 14 weeks) so we've unclipped the bottom and he just sleeps with his feet poking out the bottom. We then just cover him in a cellular blanket and tuck it in securely.
We went away last weekend and took the Sleepyhead with us, and he slept in it on the bed next to me - really easy to transport and he settled in it really well.
When I saw how much they were I was a bit
but what swayed me was a review on the John Lewis site that said something like: 'For what it is, it's expensive; for what it does, it's a bargain.' That pretty much sums it up for me. I plan to sell ours on eBay when DS2 outgrows it.
Like I said, DS2 is huge so will outgrow it quicker than most, but suspect a normal-sized baby could get a good 6-8 months out of one.
Best thing I've bought this time round and wish we'd had one for DS1 - he hated his Moses basket!