Tithe.ly Sites has amazing built in functionality that is super useful for the vast majority of churches. I think the only thing that holds it back somewhat is a more "dated" look and feel of the website design. I'm not a web developer at all, but the completed versions of Tithe.ly sites feel at least 4-5 years behind modern web pages. For example, this premium Wordpress theme for churches just looks very different http://deeptem.com/church/
However, the functionality of Tithe.ly Sites is hard to beat with other CMS (Wordpress, Squarespace) since Tithe.ly Sites has been specifically designed for churches.
Hoping that Tithe.ly invests more into Tithe.ly Sites in the coming years! Really excited to see where y'all take it.