I bought 8 of these in the 3387 flavor while they were on sale .I couldnt resist cutting one open to check it out before i started using these.Everything looks very well engineered and well built in these filters except for one thing. the spring that holds the filter in place is 3 times harder to compress than other filters I have cut open.If someone has a few of these filters and doesnt mind cutting into one check it out and see what you think about it.