Once you start doing large volume emails, using such dedicated services does make sense, they offer a lot of useful stuff, like reputation management, stats and the like. Reputation management with emails is important, you don’t want to end up in the spam folder!
Sure you can build it all yourself, but it’s a lot easier to rely on battle tested services.
As for which service, it comes down to what you need, what they offer and how much it costs. Personally, I’ve never heard of DigitalAka before, myself, I’d be checking out a range of providers before making a decision