CPI Card Group (NASDAQ: PMTS) stock is on a roll. CPI Card Q2 earningsShares of CPI stock sold off after StreetInsider.com reported the company earned only $0.17 per share in Q2, "$0.36 worse than the analyst estimate of $0.53." What this means for CPI Group stockValued on GAAP earnings, CPI stock seems reasonably priced at 24 times trailing earnings, but here's the thing: If you value the stock on free cash flow, its price-to-free cash flow ratio drops to just 4.2x -- astoundingly cheap. Should you buy stock in Cpi Card Group right now? Before you buy stock in Cpi Card Group, consider this:The Motley Fool Stock Advisor analyst team just identified what they believe are the 10 best stocks for investors to buy now… and Cpi Card Group wasn't one of them.