IMO, mylar bags are a risk, you may be abe to keep them sealed (at the top) but they are prone to ripping, tearing at a fold - and being punctured.
Mason jars are not 100% effective- but pretty damn close..and far more reliable than mylar. Same goes for tins. Almost everything I have goes into mason jars. The ONLY downside is if you choose to re-sell tobacco in mason jars you may not get full price (maybe)