I don't like this type of down-cycling - while this is good because it double-uses a single use thing extending the use of the material to another cycle this is

I don't like this type of down-cycling - while this is good because it double-uses a single use thing extending the use of the material to another cycle this is bad because it is sold as recycling to the consumer (on the milk bottle side at least). Those containers are probably easy to identify visually even at larger scales so its probably actually pick them out of the general plastic waste. The main issue with recycling plastic is that there are several plastics that just look the same until you check the embossed mark and number. This is not always easy to find / visible or even there at all. if you manage that you need to identify and remove the other plastics that make up the bottle. Many PET bottles have a shrink wrap label on them that uses a different plastic altogether. Generally it don't have a mark and can't be identified so it needs to go into the general garbage. same goes for the lid and related parts (bottles often have a ring that splits off when you open them) but realistically this does not have a mark showing the plastic type so you have to discard it into normal garbage. So basically plastic recycling while possible isn't really viable unless you reduce the allowed types of plastic and colors massively, school consumers a lot more and somehow create a cheap way to sort out the mistakes that happen. even then plastic is only good for a few cycles at best and after that down-cycling is the only thing you can do. glass, steel and aluminum do not have that issue.