Is it a good idea to use neosporin for opened blisters?
Example of opened blisters:
As per its description, Neosporin can be used for minor cuts and scrapes, which seem to fit well to your description of opened blister.
The picture provided shows a shallow opening. I doubt something like that would be much of a concern. It would be better to cleanly cut of the loose cut skin to a comfortable level and wait for the healing process to complete. If the loose skin is left uncut, it would have the risk of becoming a handle to rip the skin further. If the wound is deeper, then treat the wound as prescribed.