It's brutal and tedious to add non Google things to track to their Tag Manager. Feels like an engineering written tool, Segment.io's "flip the switches" is way better for the people that use these types of tools, ie marketers.
Hmmm...I'm not an engineer and I love Google Tag Manager. It's not the most intuitive interface, but after a few hours, I can't imagine ever managing scripts anyway else. No need to bug my CTO just to add a conversion pixel? Heck yeah.
If you're looking for another free service that's kinda in between Tag Manager and Segment.io, we built "Add This Script" (https://www.addthisscript.com/) that lets you choose from more than just analytics scripts so you can include jQuery or Facebook widgets and manage that all in one place. We add new services every week or so.
We're also working on some dependency management stuff so you can include jQuery UI and it'll automatically pull in jQuery, for example.
