hi radiok, aside from login with ajax, your plugin can also work with another plugin I have, events manager. usually recommend it to lwa users that ask, just had another play with it and love the simplicity.
one thing I've done recently is move to registration bookings, and a phone is added to the user meta. problem is, the name is dbem_phone, and whilst it'll work if we add a custom field in your plugin with that name, would be great if we could use another name instead.
one super quick workaround would be just to add a filter to line 1655, so it'd be:
$key = apply_filters('rpr_custom_field_key',$this->sanitizeText($v["custom_field_name"]));
that way, I could whip up a quick search/replace function that users can adjust.