Hi guys

I'm looking to pick up one of these for a couple receivers. Now I seem to
have run into a concern. I did some research and found several models that
don't offer crowbar overvolt protection.

The RS-3a, RS-4a, 5a, and 4L and 5L.
But, I see they have a primary fuse on back.

Now take the RS-10a. It has crowbar protection, but no fuse for a primary
overvolt. So I figured if they have crowbar, they don't need a fuse. But now
I have found Astron models with crowbar but some use a fuse while others
don't.

So what's the story here? Which one is best? One that uses both a fuse and
has built in crowbar protection or it doesn't matter as long as they have
crowbar?
Why do some use both then?

Why do some not use a fuse at all? That doesn't seem to make sense.

Thanks for replies
Lucky