I have used it and I would warn people against it unless they actually take a very careful look at the terms of service. It is a legitimate service and they do actually do a good job, but the problem is it's mining, I would avoid anything to do with mining difficulty as an investment if you can help it, you'd honestly be better off speculating.

Not only that, there's a clause they have where they basically shut down the hashpower you've bought if it becomes unprofitable and you can't build up your investment, the hashpower doesn't stack so if your profit drops you'll lose that hashpower you thought you had stacked up permanently which makes me wonder why they put it there in the first place.

So it's not 100% a scam or anything, but honestly the terms of their contracts should be far clearer and illustrated to people before they buy it, just on principle, I would advise against anybody investing in something that can be affected by mining difficulty, you won't make it.

Honestly, even putting time into Steemit and growing your account massively would be a better option :P but I can understand wanting to diversify.