I've got a Viaggio capsule and my little one still easily fits in them. The SNS Unity is a cheaper/similar concept. They're designed for 9-12kgs depending on the model I think. The SNS has been rebadged for the HiPod capsule and the Fisher Price capsule. And both capsules fit into a number of prams.

My Viaggio fits into my P&T Sport with an adapter.

I find it convenient when I'm not using my Ergo. It just makes it easy to snap and go and she faces us.

But it's pretty much personal choice and budget.