Does the spellblock from Daressos courage work well?

Wondering if it would be a good idea to get it if I plan to have around 71-75% physical block chance.

I mean when you are on low life thats when you most need the spell block.

Or would it be best to opt for general spellblock? The only thing I could muster in that case would be the 50% from lazhwar and I want to build with the anvil.

Is spellblock even absolutely necessary?

Also is the movement speed penalty from the anvil that bad? Considering I get boots with + moevement speed and you can just use leap slam to get around and escape.

You generally don't want to be on low life if playing a life-based char, so don't plan around it. And even if you build an ES lowlifer, Rathpith globe + lazwhar or rainbowstrides is the better option as daresso has no ES at all.

Depends, if you're not a spell user, spellblock isn't necessary except for the toughest encounters in the game and playing hardcore. If you are, you generally want to have it to protect yourself from reflected damage, especially from ethereal knives as elemental damage can also be dealt with by overcapping, using appropriate purity aura.

20% move speed is a serious hit, but if you got leather and steel, a few move speed nodes and good boots you won't feel it much, or you can just live with it if you like to take it slow so it doesn't bother you. There are even builds like a cycloner that don't want to have a lot of move speed as it forces them to cast cyclone more often.