Neither Google Tag Manager nor B12 offers a free trial.
Google Tag Manager is designed for Large Enterprises, Medium Business and Small Business.
B12 is designed for Medium Business and Small Business.
The starting price of B12 begins at $24/Month when Billed Yearly, while pricing details for Google Tag Manager are unavailable.
Some top alternatives to Google Tag Manager includes Viraltag, Launch by Adobe, TagCommander, Tag Governance, Tealium iQ, Google Analytics, GingerTag, TapAnalytics, Tagmate and Scale8.
Some top alternatives to B12 includes Unbounce, VWO Deploy, Wix, Jimdo, Weblium, 8b, WebsiteBuilder, Format and Web.com.