This may be more of an academic question and less of practical relevance but I hope to have some input from this site nevertheless.
In my opinion, multi-use products are always more sustainable than single-use products if viewed holistically (not just single impact categories like water use or CO2 emissions).
Sometimes when I say this, this is debated and people might say "Yes, but it's no use to transport empty deposit return bottles back to the producer if the factory is hundreds of kms away". Which probably is more of an issue of designing a product so that several producers can accept it rather than a flaw of deposit return packaging in general.
So, are there any single-use products that really are more sustainable compared to multi-use products with the same function, ignoring potential flaws in the multi-use system (like absurdly long transport distances)? And what are the biggest flaws affecting sustainability of multi-use products? For example, not-using them frequently enough and therefore a single-use product may be more beneficial?