Hi Christina,
Have been using Google Tag Manager since its launch. It is completely focused on making marketers's tasks free from the involvement of developers. It achieves the objective to a great extent.
I like it for the following reasons:
1. Once you have added Tag Manager script to the site, you do not need to go again to the HTML source for adding a script. It's pretty smooth at that function
2. It's a long term approach and can prove a great time saver for teams working on active campaigns.
3. Account management is easier - more like Google Analytics. You can handle scripts for different sites or campaign from a single platform