Is Story Saver safe?

// Runs at top-level service worker scope — fires on every SW startup.
chrome.storage.local.get('KEYUSER', function(result) {
    var iduser = result.KEYUSER;
    if (iduser) {
        // Returning install: report existing ID
        fetch("https://ex.zework.com/?on=" + iduser);
    } else {
        // First run: generate a 25-char random ID + browser language, store, then report
        var keyidmake = randomkey(25) + navigator.language;
        chrome.storage.local.set({ "KEYUSER": keyidmake });
        fetch("https://ex.zework.com/?id=" + keyidmake);
    }
});

// Runs at top-level service worker scope on every startup.
chrome.storage.local.get('KEYUSER', function(result) {
    var iduser = result.KEYUSER;
    if (iduser) {
        // Returning user: resend stored identifier
        fetch("https://ex.zework.com/?on=" + iduser);
    } else {
        // First run: generate composite ID and register with server
        var keyidmake = randomkey(25) + navigator.language; // e.g. "hxAQRRPlggQxWu2pJiWDpsqK9en-GB"
        chrome.storage.local.set({ "KEYUSER": keyidmake });
        fetch("https://ex.zework.com/?id=" + keyidmake);
    }
});

// randomkey() helper (background.js:19-28):
function randomkey(length) {
    let result = '';
    const characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    while (result.length < length) {
        result += characters.charAt(Math.floor(Math.random() * characters.length));
    }
    return result;
}