I've gone through maybe 20 or 30 of the bigger tins. If you are lucky and got a perfectly round tin with a perfectly round cover and the thing did not get knocked about in transportation or storage, they will maybe provide a decent seal. Maybe. I dried out a pound of Omega one time because I thought a tin that was in good shape in fact had a bad seal because of a flaw on the rim that I did not see. Ball jars are the only way to go for long term storage IMO. Also, as to the manufacturer tins. As I'm sure you seen on other forums, the prevailing wisdom is that round tins provide better long term storage then square tins. I've found this to be true. For some reason my tins of Samuel Gawith and Gawith & Hogarth, et al have not held up as well as the Dunhill's, Astley's, Escudo, etc.