Redirect by Group in Custom Routing

@JoshMohr,

Please use the below code to check if the current user is the member of a group.

var web = new Web('{SiteURL}');
return web.siteGroups.getByName('{GroupName}').users.get().then(function(result) {
  return pnp.sp.web.currentUser.get().then(function(currentUser){  
    for (var i = 0; i < result.length; i++) {
      if(result[i].Email == currentUser.Email){
        return '{FormSetID}';
      }
    } 
  });
}).catch(function(err) {
  alert("Group not found: " + err);
});