Why choose a sleeping baby productions sling?
I've been making slings -- and only slings -- since 2001.
There are a lot of sellers on eBay and Etsy now, many of them using the same pleated design I've been using since I started (and for which I offer free sewing directions, for personal use, and have done since early 2001).
What's the comparison?
Well, the prices may be similar and the fabrics may appear to be the same. But I feel that my years of customer service and troubleshooting make SBP a better choice than what may be a brand-new startup, where the maker in question may not be able to answer your questions about wearing your sling, or may not have considered the mechanics of how a sling is sewn.
For instance, the further away from the rings the first seam is sewn, the less the shoulder area will be able to spread out. The wider the pleats, the more unmanagable the shoulder can be, cutting into the wearer's neck and flowing over her arm. (I've seen some photos where the wearer's arm is litterally pinned to her side, the pleats are so wide.) The narrower the shoulder area is, the less you'll be able to spread it out. I've put a lot of time and testing into my slings, so you can rest assured they will fit most wearers correctly. I've seen a number of slings where the sewing is so far from the rings, even the seller is unable to wear the sling correctly -- the fabric ends up all bunched up by her neck, or in a 4" area on top of her shoulder. That's not comfortable in the long run, and can be unsafe as well -- if the rings have to be worn low for the wearer to be able to spread the fabric over her shoulder, there's less room for the baby in the sling, and less fabric around the baby's body.
Where is their fabric from? Cheap fabrics bought from "jobbers" like JoAnns and Hancock's, or from discount chains like Walmart, are not made to hold up for long. They're the "fast fashion" of fabrics, and are likely to break down faster than a quality fabric with normal use. Many Etsy sellers use linen straight from www.fabrics-store.com (you can tell because they don't even change the names...) -- which is fine for personal use, because you can keep an eye on the sling as you wear it, but I stopped using their linen years ago because I was getting way too many emails from customers that 1) their slings took forever to break in and soften, and 2) they were seeing holes open up in the linen after just a couple of wash/dry cycles. I changed linen suppliers and now have a higher-quality linen that is soft without a long break-in period, and so while my slings may cost a little more than the cheap ones on Etsy, it's for good reason.
Does the seller offer original directions? If not, it's likely they haven't fully considered how to help when a customer has a question about how to use a sling. It's my experience that in order to tell someone how to use a sling, you have to know it inside and out yourself. You have to have worn a sleepy newborn, or a heavy, struggling toddler, to really be able to troubleshoot those situations. I'm on my third "sling baby" now, and have years of experience with a wide range of ages and stages. If you email me, I'll be able to help. Will you get that kind of help from someone who is copying another company's wearing directions? Who knows. And of course, the photos used in their listings will tell you a lot -- are they even using their own slings correctly? If the rings are down near their ribs and they have to hold the child to keep them from falling out; or the fabric is all bunched up by their necks, they probably won't be able to help you wear a sling correctly or comfortably, either.
Sewing (and wearing!) slings can be a safety issue. When you buy something that will be holding your child, you want to know that it's going to be safe. Is the seller using adequate fabrics, or just something they got cheap at WalMart? If they're using thin cotton prints, are they in a single layer (one hopes not!) or safely doubled? Are they using safe rings? Sometimes they will say; other times, it's left to your imagination. And it's not something that a lot of manufacturers like to talk about, but it is important: are they insured, in case the worst happens and a child is injured in one of their slings? If they aren't insured, both parties are in for a world of hurt.
Of course, some Etsy and eBay sellers are reputable and do sew safe slings and can help you use them. I don't want this to sound like I think all of them are universally bad, because they aren't. But you need to be able to tell which are which, and examining the photos (or indeed, the lack thereof) can tell you a lot.
Good luck, and safe babywearing!