what would be those bad things ?
price go back to 25 ?
difficulty increase x2 ?
Based on my calculation even those happened this miner is still very profitable... i'd like to understand what do you factor in those "bad thing" ?
Price going back to $25 might be better for ROI than price going up to $100 (if you calculate ROI in LTC, which you should), although if there is a price drop there is no guarantee it will stop at $25. Back in 2014 LTC went from $40 to $10 in a few months.
On the other hand, if the price keeps rising and Bitmain keeps selling miners on top of the (possibly) thousands they already sold for July/August then difficulty may rise a lot more than 2x by the time the September batch arrives.
Then there is the risk of hardware defects, the risk of lending your money to Bitmain, etc.
Don't take this is an investment advice though. You asked I answered. You may have a different tolerance for risk, which is fine. I've had my share of risky hardware purchases and now I'm mostly in GPUs.