It's just replacing the old KH Donate which was a third party company. With KH Donate you could electronically transfer money to your local congregations bank account and KH Donate would take a 3.6% transaction fee. For now, Watchtower is doing the same thing that KH Donate was doing but not charging a transaction fee... but like I said... for now.
For a lot of people in our congregation they donate the same amount every month, once a month, with a check. Some are actually happy about it because they have no other reason to carry checks with them. Everything is online, credit or debit card.