At the risk of showing my ignorance, what IS a sniffer and what is it used for?
Sniffers are needed because radios tend to be too sensitive to provide useful signal strength readings when you get very close to a transmitter. For example, using a small 4 element handheld beam at 2m may result in full-scale reading in any direction because there's so much RF hitting the beam. Even loops with very deep nulls can become useless when the RF is so strong that it's bleeding right in through the radio's case, and can continue to pin the meter even with no antenna or a dummy load attached.