The current sales include (among other things) the Outrider's Token. The Stone of the Tortoise (aka XP disabler) is a kind of mirror image of this item in many regards - both are available at the same base price, both are equipped to the pocket slot, both change the rate of character XP gain to tailor the gaming experience more to the user's liking.

I'm a bit disappointed that the Stone of the Tortoise was not included in this sale - sure, it is a niche product and rather new to the Store but the players wishing to slow their XP gain would certainly have appreciated a chance to buy this item at a reduced price. Seeing the Outrider' Token discounted but not the Stone of the Tortoise feels like a bit of a let-down in a way past sales which only included the temporary XP-boosting scrolls did not.