Great thread! I'm glad you asked this because I've read and wondered the same things about the inserts and such. I used a pouch sling and a Moby Wrap when my youngest two were newborns (and young babies). I did not have a SSC at that time but now have both an Ergo and Boba G2. The Ergo, of course offers the infant inserts, and has become my preferred carrier in the last year or so (our youngest is 22 months).
I was looking at the heart to heart as well with the intention of trying to wear our newborn in the Ergo since I like it so much, and like you found a lot of negative reviews and questions or complaints. Boba G2 offers nothing like that. I asked the Boba company about wearing newborns/babies under 15lbs and was told, though not very clearly, that parents have done it without issue, that there are safer ways to do it if you're going to do it. When I prodded for more information with more information about safety and such they said the Sleepy Wrap was the better choice for newborns.
ETA: As of right now, I plan on bringing both the pouch sling and Moby Wrap to the Birth Center with me and leaving the Ergo at home.