What cucumber is this? is it hardy and safest?

Im planning on buying this for my reef tank as its available at LFS... will it eat algae on sand bed and uneaten food?

 

It consumes the sand and removes the flora and fauna of the sand, and poops out clean sand. Would not be ideal for a small tank as the cucumber would wipe out the sand bed much quicker. Part of the flora and fauna contribute to a healthy sand bed and tank, a cucumbers consumes all. The cucumber will eventually starve in a smaller tank and destroy the sand bed.

In large tanks with deeper sand beds no problem.

 

ok.... so i guess urchins are enough for my tank..... the size of cucumber is around 4-5" though...

 

is this the hardiest?