Apple’s clampdown on ad tracking has prompted some small online merchants to cut back their ad spending on social media sites like Facebook, which they see as a less effective outlet than in the past. Among the beneficiaries are e-commerce software firms that specialize in collecting data on how consumers behave on merchants’ websites—and then helping merchants use the data to more effectively market to those shoppers.

We decided to take a look at three such firms, Klaviyo, Yotpo and Rokt, each of which reported rapid growth in the past 12 months. That’s thanks to merchants like Vanity Planet, a skin-care seller. Alex Dastmalchi, CEO of Vanity Planet, said that since the spring—when Apple’s changes took effect—he has cut his ad budget for Facebook and Google by half amid “unbearable” rising costs and the privacy challenges that are reducing the return on investment. He has reallocated the money spent on Facebook and Google ads to digital marketing services, including Yotpo, Dastmalchi told The Information.