The advantage of that over an actual credit card is security and cost control: I have a separate bank account only for my Visa debit card. This account has overdraft disabled and will bounce payments instead at no cost to me. I keep a balance close to zero on this account. When I want to pay something online, I quickly do a transfer in that amount from my main account to my "Visa account", then pay. This will immediately subtract funds from my account, or the payment will immediately fail if there isn't enough (but there will be as I just transferred it).
This means my card is fraud-proof except in the unlikely case of someone managing to make a payment during the couple of seconds between me pressing transfer in my bank app and pressing pay wherever I'm paying. And even if they did that, they'd be limited to the amount of my intended purchase.
Apart from that very low worldwide acceptance, and even when it's accepted in theory, it rarely works in practice in countries not accustomed to them. For example when I go to the US I often see the Maestro logo on various retail shops or PoS machine, but I have never been able to successfully make a transaction, ever. In fact, even ATMs are sometimes hit and miss, though those usually work.
Oh yeah, and they are in general unusable with hotels and car rentals, even in Europe.
It's the same with Amex in Europe. Almost all big supermarkets (Spar, Merkur, etc) display Amex sign on their entrance, but I have never met an employee that knew what to do with Amex cards. At least Amex cards, unlike Maestro cards, have, or can have good benefits like airline miles and whatever. You get nothing with Maestro.