I bought 15 AntMiner S7's in the beginning of july for 9.5 BTC on hashnest
Earnings were about .07 BTC/day until the halving, when they went to around .01 BTC/day on average.
I just cashed out my 73 TH of power for 6.7 BTC, and was more than willing to take a loss of 2.8 BTC - explained why below
Hashnest does do real mining, but they're more cunning than other companies when it comes to ripping you off - they do it through their maintenance/payout ratio. This ratio changes every day, making earnings quite unpredictable.
I failed to take into consideration the possibility of Hashnest maintenance/payout almost tripling after the halving. I don't believe that this fee is genuinely what Hashnest has to pay on power and real estate. I truly believe that this fee is arbitrarily set by Hashnest as determined by the profits they wish to make per day, knowing that you have no leverage over them once you've paid for your miners, they "have you by the balls", knowing that you'll be forced to take a loss if you don't pay their ridiculous maintenance costs.
At the time of buying I assumed that the difficulty would either decrease or remain around constant -- and also less miners on AntPool -- and thus would increase your share of bitcoins that were mined, despite the halving, and I was correct about that. Problem is, the Hashnest maintenance fee will completely destroy your investment (currently at 81%)
If the difficulty was projected to continue to decrease, I probably would have stuck around, but the next difficulty I think will increase pretty significantly, which may cause the maintenance fee to go around 90-95%, depending on BTC price
So when you mine on Hashnest, you have two factors working against you: 1. bitcoin difficulty and 2. the hashnest maintenance/payout -- this makes your investment extremely risky and unpredictable
Ultimately, I highly recommend you invest bitcoin into other areas, NOT Hashnest, as they have total control over your earnings via their maintenance/payout ratio which changes every day. Most days after the halving were embarrassingly bad.
The big problem I have with Hashnest is that they can decide at any time to increase their profits by increasing their maintenance/payout ratio to arbitrarily high levels, and there's absolutely nothing you can do about it, since you've already paid for your miners. There's no way to verify that they're being honest about their maintenance costs (even if they are, why invest into a company who needs to take 90% of your money for maintenance?). Talking to people who run their own large mines, the Hashnest maintenance cost seems insanely high, especially for operating in China who has some of the cheapest energy costs. The Hashnest customers have no leverage over them. That is dangerous in my view as they have no motivation to make changes to facilitate a cheaper maintenance cost.
I would have stayed with Hashnest if they allowed you to convert 3 S7's into 1 S9, but they recently announced that they will not allow this, making your possibility of meeting ROI about 0% considering the difficulty will be increasing in the future... You will probably be earning 5% of what your miners generate in the near future.
Some may think S9's will still be good, but I don't think so. I think they will be far overpriced, as they have no competition, and by the time you're remotely near meeting ROI, difficulty will be sky high and you'll be in a similar situation
Hope it helps