You can send Tom for everything except BEM, SEM and LEM.
He offers you a maximum of 7, 8 or 9 items. Don't settle with less then 9. Say no to his offer, he will rest for 2min and you can send him again for the same item. Sometimes it takes 5 times, but eventually he will bring you 9 items. And after that he will take a 2hrs nap :)
Edit: I don't know how many diamonds you have ofcourse, but if you hire Tom for 10 days (100 diamonds), and you rehire him again it 'only' costs you 70 diamonds. This special offer only lasts a few minutes.
I bought some diamonds during Christmas brake (3months ago), hiring Tom ever since and I still have about the same amount. I regain a lot by mining, leveling up and the diamond toolbox.

