I would recommend against it. They become a real pain down the road.
I wish I had something to suggest as a replacement. We're still trying to figure that one out ourselves. We just know we won't use submodules again. For now, we're manually managing disjoint repositories.
The replacement is definitely the article's first suggestion: Cocoapods. Cocoapods is awesome and is rapidly being adopted by major repositories like AFNetworking, Kiwi, TTTAttributedLabel, MagicalRecord, and more: http://www.cocoacontrols.com/cocoapods
It has been super easy compared to git submodules.
The first thing you should do is fork the repository and set up a remote for pulling in upstream changes.
There are a lot of useful libraries out there, but I find I occasionally need to make changes. Sometimes there are bugs; sometimes the maintainer has lost interest. I need to be able to pick up the slack when that happens.
I wish I had something to suggest as a replacement. We're still trying to figure that one out ourselves. We just know we won't use submodules again. For now, we're manually managing disjoint repositories.