Tomarto puree seems to add a sweet tomarto flavour, whereas blended tinned toms add a sour tomarto flavour, the latter being particularly evident if they are added AFTER the base, rather than being fried-in in the initial stage (which is what most people do with puree). That works VERY well for hot madras type curries. Passata works equally well, if not slighty better, than blended tinned toms in that application. I swear by it!