Ofcourse one have to have the same resistance with the components, especially the aircoils and thats gonna be rather expensive. DIY can be fun and can be good but can also result in no better sound and a lot of work.They really need to have something like TV's where there is a 'demo mode' setting so the picture looks good in the super bright store. Because the better speakers often sound bland in the store.
Buried in all the BS he probably has some good points but it is hard to put any weight into what someone says when you have to filter out so much of what they say. He is the classic example of a little bit of knowledge and a little bit of fact mixed in with plentiful BS so it sounds better.
It makes me cringe slightly when I see him referred to by people as an expert.
I still think the people that just blindly switch out coils and capacitors have to be careful as they will end up with different resistances and it will affect the overall function of the crossover.
People that do measurements on the changes don't risk that but I think his videos lead a lot of inexperienced people to break open the crossovers in their speakers and spend a lot on 'upgraded' components.
The number one thing I see as a comment from people that replace electrolytic capacitors with poly is 'more detail'. Well, a poly will have less ESR so a bit more power will make it to the tweeter to increase the highs and thus... detail. And if they are replacing a really old electrolytic it may have been functioning more as a resistor so the difference will be even more amazing. Similar thing with changing iron core coils to air core. If you replace a low resistance iron core on your woofer with a higher resistance air core then the woofer will get a tiny bit quieter and again, the highs will stand out more.
The measuring and matching cheaper resistors is a great way to get more accurate parts without spending a fortune.
A good measurement mic and a good loudspeaker program is a must.