If Wit's end built out of Negatron, you would lose MR on the upgrade. Rather, Wit's End should keep the Nullmagic Mantel build path, but Recurve Bow should be boosted to 35 or 40% AS increase, and build out of Dagger. As it is, if you don't have enough money to upgrade into the item you want, buying a dagger as part of the build path feels like it doesn't help much, giving minimal AS boost, while taking up an extra item slot which could be used for wards and pots. Especially BOTRK, which you would take up two item slots, for the same bonus as you could get with another item, but that item doesn't fit into your target item's build path.