While I wouldn't buy a chain checker, there's no reason no reason to discard or not use one that's already aid for.

Take a hint from the medical community, where a simple test that tends to false positives is used to screen, then if there's a positive, they follow up with a more reliable test to confirm or deny.

Likewise, use the chain checker to quickly verify that the chain is NOT stretched, but when it starts to show stretch, confirm with a ruler before replacing anything.