The important thing with cutting open an oil filter is to know what you're looking for, and identifying what you find. Pour the oil in the filter through a funnel lined with paper towel and let it drain for an extended period to see with better clarity, what was in the oil.
Check the bottom of the filter can and spray it with some carburettor and throttle body cleaner, to separate the carbon and other deposits from the heavy metal components. Scrape the bottom of the can onto more paper towelling and let it drain.
Spread the filter element treated paper out on paper towelling and let it drain. Run a magnet on an extension wand over the gunk to see what sticks to the magnet.
Aluminium particles are bright and easily seen. Iron particles attach to the magnet. Copper particles are ... well, coppery colour. Rubbery bits are pieces of gasket material. Chrome (from ring faces) is harder to identify, because it can look a bit like aluminium. Chrome, of course, is largely non-magnetic, but it depends on the alloy, and whether what it was plated onto, is still attached.
But the important thing is, the size of particles. Very small particles shouldn't be concerning, they are part of normal wear patterns, but chunks of metal, and substantial amounts of coloured metals, or serious amounts of iron particles on magnets should raise concerns.