Preorders for the $150 wrist tracker started in late August, but the device has been hit with some mixed reviews lately. Gizmodo called it the “best fitness tracker, period,” but The Verge said it was plagued by bugs.

In a report on Thursday, Pacific Crest analyst Brad Erickson said he checked with 15 major U.S. retailing chains and heard that demand has been lukewarm so far.

“Our checks are already finding meaningful inventory accumulation in the channel; more than two weeks of inventory is on hand,” wrote Erickson. “While sell-through should ramp meaningfully as the holiday nears, Charge 2 run rates are below where Blaze and Alta began earlier this year, which is a disappointing start, in our view.”

Shares of Fitbit, which had rallied almost 40% over the past three months, were down 5% in premarket trading. The stock is overvalued by about one-third, Erickson said, downgrading the company to a rating of “underperform.”

The new Charge 2 updated the best-selling fitness tracker on the market. The new model added a much larger tappable screen, better sensors to automatically distinguish different forms of workouts, and closer links to a user’s smartwatch, including using the watch’s GPS sensor to track movement. At the same August event, Fitbit (FIT) also introduced a simpler band, called the Flex 2, a line of fashion accessories and a new online component, dubbed Fitbit Adventures, to get consumers more involved.

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Fitbit’s new products in the spring, the $200 Blaze and $130 Alta, got off to a fast start, with the company saying it shipped 1 million of each in the first month they were available.

The company’s stock has been on a tear since it posted better-than-expected second quarter results and CEO James Park promised profit margins would improve. But even at Wednesday’s close of $16.70, the stock remains about 17% below its initial public offering price from last year.