If mining is indeed profitable, why should they sell a slice of their profit for a fair price?
Either the price is unfair, or it is just a scam.
Of course, they might be selling shares of the mining profit for fiat money immediately needed for maintenance, or for acquiring new gear and so on, but it's a very long shot. I'd imagine they should have their cash flow under check if they're so successful. And I've never heard of current mining gear being sold on credit. On the contrary, it is usually paid before delivery - often much too long before delivery.
TL;DR I reckon you'd be better off investing your subscription fee directly in bitcoin.