In the nation’s battle against the diabetes epidemic, the go-to weapon being aggressively promoted to patients is as small as a quarter and worn on the belly or arm. A continuous glucose monitor holds a tiny sensor that’s inserted just under the skin, alleviating the need for patients to prick their fingers every day to check blood sugar. The monitor constantly tracks glucose levels, sends readings to a patient’s cellphone and doctor, and alerts patients when readings are headed too high or too low. Nearly 2 million people with diabetes wear the monitors today, twice the number in 2019, according to the investment firm Baird. There’s little evidence that continuous glucose monitoring (CGM) leads to better outcomes for the estimated 25 million U.S. patients with Type 2 diabetes who don’t inject insulin to regulate their blood sugar, health experts say. Still, manufacturers, as well as some physicians and insurers, say …