Geode or Nodule or Thunderegg or ?? Options

[JJCA]

Hello. I am new to this resource but hoping you all can help. I inherited my grandfather's rock and mineral collection years ago -- he grew up in Leadville and his father ran a dry goods store-- miners would often trade some of their finds for goods. I am unpacking some of the stuff and am not sure what one of the specimens is. I believe it is likely a geode or thunderegg but am not sure. It is a little larger than a softball and feels rather heavy (not super hollow). I have a neighbor with a rock saw that has a diamond blade and he said I can use it to cut open the rock. Does anyone have advice or guidance for doing so -- specifically in terms of how to get the most ideal cut to show what's inside, or is it mostly just luck if there are no real defining exterior features that would provide a hint? Is there any reason not to open the rock (in terms of losing its "value" or causing significant damage to it)? Thanks so much for the help in advance! Two pics attached.

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