This usually means you already have a reason to ask, which is a better starting point than a broad panel.

A single-contaminant kit uses the method that suits that one thing, so the detection limit is where it needs to be instead of being averaged across a long list.

Arsenic and nitrate are the usual two on a Michigan well. Lead is usually about the plumbing and the service line rather than the source, so how the sample is drawn matters.

Do not buy a filter before the result. A pitcher or an under-sink unit is rated for specific contaminants, and picking one without a number is guesswork.