No offense, but I was under the impression that you inflate safety sausage ON THE SURFACE, not UNDERWATER. Afterall, it's a marker device to enable for surface support to see & pick up a diver.
It is great to inflate the SMB while ascending. Not only does it give a heads up as to your position, but it helps with the safety stop. I inflate at the 15 foot depth. I have 15 feet of cord with a loop attached to the SMB. Once it's at the surface, I can go slightly negative and simply hang on the bouy. It is wonderful not having to watch your depth guage all the time. As I'm always in clear water, I can watch the goings on on the reef far (or not so far) below. An effortless and enjoyable safety stop.
Just make sure that you don't fully inflate if your SMB doesn't have an overinflation valve.