As good as baby bjorns appear to be in terms of being hands free, they are actually extremely bad for a babies spine.
Anything that supports a young baby by the crotch (such as jolly jumper, walker, carriers such as baby bjorn) put pressure on the lower spine. They are completely unsuitable for a newborn. By the time a baby is big enough to be supported by the crotch they have outgrown the baby bjorn.
You will not find a chiropractor that supports th4e use of a baby bjorn.
Even the walkers and jolly jumpers say not to use them for more then 10 mins a day.
If you want a carrier in a similar style - go an ergo. they have an infant insert that you can use that supports all of the babies spine and doesn't concentrate the weight on one spot. I bought one after my first and Iuse it to carry my 4 year old in as well- so it will certainly last the distance.
I bought mine second hand for $80from ebay and it had been used only a few times. there is no need to buy a new one. (although I definately think $200 is worth it- although that is the most expensive ergo I have ever heard of, they are usually up to around $150 at the most)
In terms of slings - be careful not to put them all in the one basket. There are so many different types of slings and they are all for different purposes. Various types suit various activities and what you find comfortable somebody else will hate. Lots of people try one dodgey cheap thing that kills their back and suddenly all slings are dismissed as dismal failures. In reality if a sling hurts you are either wearing it wrong, you are using the wrong sling for the activity or its bad quality.