Well, Ferrothorn is a notable user of Gyro Ball, and it uses its poor Speed and great Attack to be probably the best user of Gyro Ball out there. Also, yes, Gyro Ball is a pretty good move in competitive.
Now, a set.
Ferrothorn @ Rocky Helmet
Ability: Iron Barbs
EVs: 252 HP, 252 Atk, 4 Def/SpDef (for a more bulky Ferrothorn, replace the attack EVs with Def/SpDef and put 4 in the defensive stat you didn’t use)
Nature: Brave (+Atk, -Spe)
IVs: 0 Spe
Stealth Rock is for entry hazards, Power Whip is STAB, and Leech Seed is for healing. Gyro Ball is great on Ferrothorn due to it being STAB, and Ferrothorn has awful speed.
So yes, I’d say that Gyro Ball is a very good move, and I recommend it on Ferrothorn.
Hope this helps! :)