Thanks @sanderjansenart! I am not a big instagram user so in a way it is not specially interesting for me neither. But in a way it makes simple posts still interesting and shared through a community of similar, short posts. So for people who have less time to invest and/or who are a bit scared of the complexity, I think it is a great step/interface to make Steemit more accessible to new users.
Also, personally, I was looking for an app (for smartphones) that would only use the posting key because I don't want to use my active one on my phone.