1. Tags or scripts are served asynchronously and synchronously both All the tags are served asynchronously only
2. Complete integrations with Google Analytics, Adobe SiteCatalyst, and Adobe Test & Target is provided No support for tools like A/B testing, surveys, personalization, product recommendations, or tags that require multiple snippets in different locations of the page.
3. DTM allows to capture variable from anywhere of the page Each variable is stored manually and available for the same page and can’t be captured from other pages
4. It is not completely free available It is available free of cost, anyone can start using it
5. It is not easy to use, training is must Slight study can make you use GTM
6. DTM and Adwords synchronization is not that great GTM and Adwords synchronization is awesome
7. Testing is complex Testing is very easy