I think you already know the answer. I may not have 100% success in tendering every share I purchase. So I prefer to wait to acquire new shares since I believe price will drop. I am willing to wait for a discount and I am willing to risk not repurchasing.
If, however, I already held shares (and we assume an efficient market for SPWRA), odds favor me tendering a fraction of shares that returns a net profit exactly equivalent to the profit I would get selling on the open market. Since the odds are equal, I would roll the dice and attempt to tender quickly because there's more potential upside in doing that. In other words, one might beat the odds. However, there's also more downside risk. For an arbitrageur, the two paths are equal (by the efficient market assumption). But I wouldn't be looking to arbitrage, I would be willing to risk being left holding some of the shares and wait for a selling opportunity of my choosing.