"Too cheap" sounds a fair comment to me if the price is free. Anything free is almost certainly a loss-leader, as providing the service itself is almost certainly not free (whether it's a tiny-but-non-zero bandwidth cost, or the costs of providing support).

So long as the loss-leader is paying its way via the upsell, it's fine. And if those businesses have contingency plans for moving if BitBucket shuts down the free plan, then it's fine for them too. But the fear is that "too cheap" companies also tend to be cheap when it comes to managing contingencies.