I suppose thinking about the last several posts, all I really do is put a familiar blade in the razor and do at least four shaves. Then I switch to a blade that I am less certain about and I can usually make some informed guesses about the blade since the memory of my familiar blade is fresh in my head. Sometimes, the first shave isn't very good and it takes a second or third shave to get a realistic idea about the blade. The fact that it isn't performing at it's best out of the wrapper definitely factors into my opinion about it just as the decline curve does. I have no patients for blades that don't perform their best until sometime on the second shave, it better start waking up by the end of the first shave for me! Others want a blade to last a full week, this used to be a thing I read all the time, and think that it's OK for the first two full shaves to be sub par. Further, if I only used a blade once, I wouldn't have enough time to learn anything and I guess I would use a tuck of them before deciding. I usually follow up with a blade that I think the new blade is closest to and may go back for another after that! An example of this are Dorco Primes which I consider to be a sharp minus blade, not a medium plus. I immediately followed up with a Nacet to confirm that they perform close, but the Nacet is sharper(blade feel is very close).