I'd have to dig out the stats but, depending a bit by country/market, I'd be amazed if most people didn't prefer to pay by credit card rather than DD. You might understand 'continuous' as a benefit (certainly to you as a business as higher renewal/success rates) but all the evidence I've ever seen suggests people really don't want to give anyone 'direct access to their bank account' via online DD except for charities and a few 'essentials'. I'm sure you know that insurance is seen as a grudge purchase... ;)

If you're only offering DD payment then I'd wager you are losing a *lot* of sales as a result. PayPal, of course, also offer credit card transactions capabilities, not just PayPal payments.