Comparing an urchin to snail/crab for CUC

[Miami Reef]

How do urchins compare to snails and crabs for algae? Do they act more like crabs or like snails?

Reason: buying a harlequin tusk and am expecting most (if not all) my snails and crabs to go.

Bonus question: are nassarius snails safe from harlequin tusks?

 

[reefinatl]

Odd question but i gotta say if you add spines to the clumsiest and hungriest turbo snail you've ever owned you're almost there.

 

[Spieg]

An urchin will eat more algae than any 10 crabs or snails combined. Only problem is they grow too large to get into small spaces.

 

[vetteguy53081]

Tuxedo urchin is a good worker and unlike other urchins will not drag frags around the tank.
crabs are hard to trust