Just to second what donpdonp said (https://news.ycombinator.com/item?id=6509604), I think a service like this needs to offer a standard format WARC (http://archive-access.sourceforge.net/warc/) download.

The whole point of a service like this is long-term access and that really requires a data checkout option which can be used with other tools (e.g. https://github.com/alard/warc-proxy).