Shaco's ult needs to:
1) Correctly mimic items.
2) Mimic particle effects.
3) Appear in a random location relative to Shaco.
Until these three issues are fixed, the clone will never be useful. Right now, any single issue allows other players to see straight through it with ease. And honestly, even after they are it will still be mediocre at best.
Shaco is one of my mains and favorite champions and after a while (even despite all the bugs) you can manage to find some really insane tricks with your ult (not just the dodging part) that would otherwise not be possible if the clone appeared in a random location relative to Shaco, instead of always appearing on the same spot relative to Shaco as it is now.
I think this point is not a problem with his Clone, considering in a real match finding out the clone 'just' for this is almost impossible since if the Shaco player notices the enemies are doing this he can simply quickly turn around before ulting for the Clone to appear on the other side and confuse the enemies, they wont be able to see you turning around if you do it and ult quick enough.
But it would certainly kill the hidden tricks I mentioned not to mention I for one absolutely hate RNG based abilities!
Shaco's ult definitely needs revision though. Items, buffs, post-death reliability, explosion damage, showing pings over it's head like the real Shaco (easiest way to tell the real from the Clone atm, besides buffs ofc), etc.