Definitely worth risking it. If you put Shell Smash on a Cloyster it's not meant to be a tank. It's turned into a sweeper.
(Quoted from trachy)
Gen V
Cloyster (M) @ Focus Sash
Trait: Skill Link
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
Icicle Spear
Rock Blast
Shell Smash
Razor Shell
Okay then, Focus Sash allows you to get up Shell Smash. Now you have Skill Link, which makes your STAB Icicle Spear and Rock Blast do a ton of damage while also breaking through Substitute, Sturdy, and Focus Sash. Razor Shell provides STAB, and also has a good chance of lowering the defense of the foe, which could be helpful for foes with defense boosts or resistances. Standard sweeping EVs.