Difficulty will rise like crazy. There is a masive batch of L3+ coming next month and another one the month after + more miners that we don't know of. By the time you get your Sept 13-20 batch delivered you looking at probably 2x or 3x today's difficulty (or more, you never know).

Knowing Bitmain, there are going to be more batches coming out after yours so the difficulty will constantly increase. There are other scrypt coins to mine as well but you never know how the exchange rate will be. It is all a risk in crypto world.

On the other hand with electricity that cheap it might be worth investing. It is up to how you view and tolerate risk. But always try and make your calculations considering the difficulty increase.