Does using a electrical device that is connecting to a series of power extension safe?
It's all about the current ratings.  The wall outlet has some maximum current it can deliver safely.  A fuse or breaker should pop if you exceed that, so that should take care of itself.  However each splitter may have a lower current rating.  Anything plugged into a splitter must not exceed the current the port is rated to, and together will the other devices plugged into the splitter what the whole splitter is rated to.  These generally don't contain a fuse or breaker, so will just catch fire and burn down your house if overloaded.

This logic proceeds down the tree with each new device you plug in.