For an individual...for any given profitable timeframe, if the product will not produce more btc than it cost to purchase initially, then it is not a good investment.
I was alluding to things like 0% interest rates, or balance sheet tricks like buying miners, selling one btc before end of Dec, then claiming a miner price as cost basis to claim a loss, but then sell Jan and not have to pay on the gains for a year and use that money to make other money.. that's the whole time-value-of-money
there are deeper and sketchier things going then these examples