VM 2 does handle the related products in a different way than VM 1 did. VM 1 had a table for related products while VM 2 uses the customfield table. That produces a lot of problems for big shops with a lot of products. Did try it with 30 000 products, each with an EAN code and warranty as custom field. That produces 60 000 entries in that table. There are a lot of related products, about 150 000. So we receive a table with about 210 000 entries. Not that it is a problem to import such an amount of entries it slows down the frontend pages too by querying the database.
An example:
VM 1 did it in the vm_product_relations the following way:
product_id: 123456 related products: 95645|321456|785445|5645645
VM 2 does use an extra entry for each related product. So if you have 30 000 products and maybe 100 000 relations you receive 100 000 customfield entries (only to create relations). Two additional customfields for each product with other information does create 60 000 entries.
In that case VM 2 does not a very good job. It is very slow while filling those things into the database and displaying it to the customers.
I found it slow in vm1.1! So I got rid of it.
I shoe horned in sphinx search to do site searching and realised that I could use that for related products as well. I no longer have to set related products I let the search do it for me.