Maybe my information is out of date, but the only reason I continued the sign-up process when I got to the payment page is because I have just set up a new bank account for travel money that will never have a lot of money in it, and I was able to use the debit card for that account.
I have since found that you do actually offer direct debit payment - the sign up page makes it sound like this isn’t even possible. So normally I would have stopped the sign-up process and written off Bulb as unusable.
If I had used my main bank account card and the details got stolen then the thief has the potential to empty my account. From what I’ve heard it’s much harder to get a refund from debit card fraud than credit card fraud, and in the meantime your main bank account could be empty making it much harder to carry on as usual while things are resolved. For these reasons I never give my main account debit card details to anyone online.
Hopefully you do have good answers to these concerns, and if so, I’d consider putting a bit more information in your sign-up process as I can’t be the only person turned off by the debit card requirement.