Rocker shaft hold downs

I was wondering what everyone thought about the A/m rocker shaft hold downs for a small block with factory adjustable rockers? I see that mopar performance and Hughes engines has different kits,witch one is the best? Do you think they are needed in engine that will have about 300 pounds of pressure with the valve open? Do they help in the correct rocker aligment? Just a few questions I had on this so let em know.
Matt