If the shipping is transparent in all ways and the costs “normal” then I guess it’s no different to before..I post small parcels and it will not change things for me in the main 

however I don’t like their enforcement of sending something tracked when it becomes a lot more expensive 

not everyone’s paranoid about dishonest buyers and they are few and far between 

Also
ok let’s say you sell a postcard /knitting pattern/comic/ etc it’s under £10 and under 100g

why does it have to fit in an envelope

what is it about large letters that transforms that item into a bigger risk

people who buy these items don’t expect to pay the higher postage costs 

because they have said large letters MUST go tracked