He will inflict a lot of damage in a short time...but will only last a very short time.
I used to use a C/P Alakazam at lvl30 to do exactly the same thing, prior to the rebalance...but he was a lvl30 when he was evolved so it didn't cost me any stardust.
There are better things to spend your dust on, but if you have a massive hoard of stardust then I guess that isn't an issue.
All things considered, I wouldn't do it personally as dust is too valuable.