I'm surprised Smmenen hasn't commented on this deck. After all, it was him who said it was a mistake to not play mishra's workshop in a deck that wanted to abuse Mindslaver. It still makes me laugh today.
Now that I got that out of my system for now, I'll get to my points. At no point have I ever seen any advantages Workshop Slaver has over Control Slaver. IMO Workshop slaver is fundamentally flawed. Trying to cast expensive spells in type 1 may be fun, but it certainly isn't consistant. Drain is a huge problem that is not handled by simply running chalice. Workshop does not activate slaver, or help dig for more mana. It has always appeared to me to be an all or nothing strategy that has historically produced much more nothing that all.
In my experiance, casting non artifact spells in a workshop deck is a difficult task. If you're set on running Mindslaver in a workshop deck, I'd advise adding one to a solid Stax list. It would add the lock of Slaver/Penatvus/Welder or Slaver/Crucible/Darksteel Citadel/Wedler. It is the kind of card you can tinker up in a tough spot, or even cast late game. Perhaps you'll have more luck with it in more of a supporting role instead of eating up 3 maindeck slots.
workshops are essentials to cast chalice for 2 early in the game.
this is the best proactive defense ever for this deck. in one shot you block a lot of archetypes, from c.slavery to oath, passing through t1t draw engine and so on...
workshops let you cast early a gilded lotus(first turn too with a mana vault/crypt or 2 moxes or lotus), in this case became not so difficult to cast a colored spell.
workshops let you cast easy a big treat (like pentavus, memnarch and titan).
workshops help you to survive trinisphere(to cast moxes and other mana-artifact).