They are similar in that they both are buckle carriers but are otherwise pretty different. I have a long review of the ABC in my blog (linked in siggy) - briefly the biggest differences....the Action baby carrier is much lighter weight and less structured, the waist is padded instead of stiff like the ergo, you can cross the ABC straps behind you in a front carrier; the ergo's must be worn reverse backpack style. I much prefer the ABC as I like less structure. The body sizes are similar although ABC has a toddler size which is a better choice for bigger babies and toddlers.
Re: Action vs Ergo?
Breastfeeding Counselor with Breastfeeding USA
Babywearing Guide ** Newborn Carriers
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Safe Bed Sharing Info