Magento – Customer delete before observer

You have an error in your Observer class because Mage_Adminhtml_Block_Cms_Block_Grid should be Mage_Adminhtml_Block_Catalog_Product_Grid

However you are also right that there is a better event to use, you can use 'adminhtml_catalog_product_grid_prepare_massaction' so you can do the same code but without the instanceof check and that will do what you need.

That said... I obviously don't know why you want to do this but I imagine if I was doing it it's because I don't want person X to accidentally remove a bunch of products. And so you could go a little futher and remove this action on a user basis by adding it as a acl configuration and checking if that user is allowed in the observer as per below.

etc/adminhtml.xml

<?xml version="1.0"?>
<config>
    <acl>
        <resources>
            <admin>
                <children>
                    <catalog>
                        <children>
                            <products>
                                <children>
                                    <mass_delete>
                                        <title translate="title">Mass Delete</title>
                                        <sort_order>10</sort_order>
                                    </mass_delete>
                                </children>
                            </products>
                        </children>
                    </catalog>
                </children>
            </admin>
        </resources>
    </acl>
</config>

Model/Observer.php

<?php
class NameSpace_ModuleName_Model_Observer
{
    public function isAddProductDeletePermitted($observer) {
        if (!$this->_isAllowedAction('mass_delete')) {
            $block = $observer->getBlock();
            $block->getMassactionBlock()->removeItem('delete');
        }
        return $this;
    }

    protected function _isAllowedAction($action)
    {
        return Mage::getSingleton('admin/session')->isAllowed(
            'catalog/products/' . $action
        );
    }

}

Use customer_login event observer for customer login action

1) Create events.xml

app/code/Vendor/Module/etc/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="customer_login">
        <observer name="customer_login_observer" instance="Vendor\Module\Observer\CustomerLogin" />
    </event>
</config>

2) Now create observer CustomerLogin.php

app/code/Vendor/Module/Observer/CustomerLogin.php

<?php

namespace Vendor\Module\Observer;

use Magento\Framework\Event\ObserverInterface;

class CustomerLogin implements ObserverInterface
{
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        echo "Customer LoggedIn";
        $customer = $observer->getEvent()->getCustomer();
        echo $customer->getName(); //Get customer name
        exit;
    }
}