I'm sure PayPal is wonderful for those who have never experienced an issue with their service, but for all others, they're a nightmare to deal with.
Even those who have never had an issue cannot claim that direct bank transfer is more secure, more reliable and easier than PayPal payments, particularly in terms of domestic currency transfers.
Quite aside from that bank transfer is just more convenient than any third party solution, both for incoming and outgoing payments, as incoming payments go directly into the bank account automatically, and outgoing payments are fully within the control of the person making the payment.
Okay so PAYM would have made it even simpler if they had an API companies could use which unfortunately eliminates that particular idea, but PAYM is just bank transfer using mobile rather than account and sort code numbers anyway, so it's the same thing and that can be automated and/or batch payments can be made.
Like I said, in terms of the complaints about PayPal will reflect negatively on giffgaff because although giffgaff have done nothing wrong, reality and perception are often two different things.
If all that's not enough, the more payment options available the better, (incoming and outgoing), so the customer has more choice over how they control and find their account.
And if all of that still isn't enough, all the companies these new packages compete with, I think with the sole exception of Tesco, offer payments via bank transfer.
And if all of that isn't enough, giffgaff are the only company in that bracket of packages who make you either buy a voucher or choose between handing over card details, (which they've been known to store despite being told not to), or force you to deal with an intermediary, (and give said intermediary unfettered access to your bank account/cards, not to mention a ton of personal information).
And if all that isn't enough, when you have funds due to you, they're the only one forcing the use of an intermediary to withdraw the funds, and the only one who give you no way of ring fencing account credit in some way, so that it isn't eaten by out of bundle usage, (although Tesco don't really shine in this particular area either capping overspend rather than preventing it like most others). This second issue is particularly important in respect of lost or stolen devices because there's nothing to stop a miscreants burning through account credit, unless you withdraw it.
So multiple convenience and security arguments, plus lacking in comparison with who they're competing against package wise, in those particular arenas and the image/perception issues the complaints have the potential to cause.
I wasn't personally affected by the PayPal deviousness/idiocy by the way, that's not why I'm promoting the introduction of this. I'm promoting it because it is basic common sense to skip the middle man and their inherent flaws, (convenience and security).