Just so …
Retail forex deposit bonuses are [I]very[/I] useful indeed for all the scammy, lightly-regulated, offshore, counterparty market-makers pretending to be forex brokers: they’re one of the major methods they use to identify and attract “victims”, i.e. naive, inexperienced customers who are inevitably most easily parted from their money (in other words the exact ones of which they need a continual turnover to survive, given their own business model).
To those slightly better informed, deposit bonuses (and perhaps especially no-deposit bonuses) can actually serve as a useful red flag denoting “brokers” to avoid.