Hey there, I'm one of the technical cofounders of Giveffect. Good questions!
The reason why our clients are choosing the "all-in-one" solution is because they are fed up with disjointed systems. Why shouldn't their fundraising pages on the frontend automatically talk to their CRM on the backend? Our solution is integrated in the "NGO's website automatically" as we are a complete white labelled solution powering the entire fundraising/crowdfunding/campaign-style experience on their own website.
The email marketing solution is something we're still building out, and while still in the early stages we have integrated with some cool patent-pending technology that provides deep insights and analytics. We can gather data such as which subscribers have read the email, how many times, duration spent reading the content, on which device, location opened, whether or not they clicked through any links, and furthermore converted. All of this feeds back to our integrated CRM to further segment high value, highly engaged contacts.
Currently we use PayPal as our payment gateway because they were the only ones to offer a low NGO rate for our clients. Plus they have a long standing trust with nonprofits and donors, and most NGO's already have a PayPal account with many using it as their donate button, making it an obvious choice.