lol i will try explain: i started hand-pick my switches for a particular build after i found out stock switches do have different BOM, especially springs, e.g., there are two different stock springs in gateron white 67g that i have. one is shorter with lesser coils; another is longer, with more coils. to eliminate potential inconsistency due to springs, i just choose one of them for the same build. (this is also why it's better to get more switches than you need for a build). alternatively, i can just grab a bag of custom springs, and replace them all together. so i decided to do a little experiment.
i started with stock switches with stock springs; then i tried chinese-made springs; and finally branded custom springs. i chose 65g, with gateron yellow stock springs as reference. they are all linear-rated springs.
the key observations from this experiment are as follows:
1. the differences between the first two (stock vs. chinese-made custom springs) are mainly related to weight. chinese-made custom springs are similar to stock springs ('hard' in nature, pingy; the 'hardness' in feel, i believe, is mainly due to the characteristics of spring materials and similar designs). to me, they feel the same, but chinese-made custom springs provide a wider range of weights to cater for our needs, hence they got the weight part covered. also, for chinese-made custom springs, inconsistency in spring weight happens more often;
2. when i went for branded custom springs, the scope to cover have changed. on top of spring weight, they have unique spring designs and innovations that can change switch feels and sound further; the consistency in spring weight is covered too.
you will definitely feel the obvious differences between a build of gateron yellow with stock springs, one with chinese-made 65g, and one with tx 65g. (the first two are harder to differentiate, at least to me)
edit:
honestly, the more you go into details, the more you will find out about shitty stuff like this. as consumer, we expect manufacturers deliver according to specs. unfortunately, it's really not the case.
on a greater scheme of things, most people will treat this as insignificant deviations. it's ok because we all still survive hehe (let's embrace these perfect imperfections

)