at tgc direct or at steam, both are good offers with little bit different content.
steam apps associated with your steam account, if you start it there is always a steam service in background
but is seems you can start the agk editor exe (ide) without steam direct from folder.
advantage of steam are the software updates , disadvantage is the steam dependence.
my experience with steam over some years, they have a very good service.
just saw at tgc web site
Quote: "Please note, this bundle is supplied as a Steam key which will unlock the bundle for you on Steam. "
AGK (Steam) V2017.01.09 : Windows 10 Pro 64 Bit : AMD (16.12.1) Radeon R7 265 : Mac mini OS Sierra (10.12.2)