While with traditional databases i would not recommend using bi-directional relations, with Bubble I dont think it can be considered bad practice.
Bubble does not offer the ‘join’ functionality. Without it, handling relationships becomes quite a lot more annoying, proper database normalisation is not really possible in most cases, and the industry recommendation of never duplicating data on different tables does not hold as much.
I think bidirectional relationships have their place in Bubble for now. Hopefully an operator similar to a join will come at some point but i do not see it happening soon. I think you should at least consider linking both tables to eachother, in some cases it does work well.
You can use Trigger Events to make sure that relational fields stays consistent between the two tables.
As @tylerboodman mentioned, lists can become problematic if multiple users can edit them concurrently, OR if you expect that the list could become larger than 500 elements (debatable number).
Lists can be great for use-cases where the above problems do not apply, as they are faster than searches, and much more easily sortable. Sortable searches are a pain.
This could be helpful:
Exactly 
without the join operator you cannot effectively filter without having some sort of redundant fields. I sometimes duplicate the filterable parent fields onto the child elements. Someother times I use bidirectional relationships instead and reference the Parent’s list of children. In the end it depends on the particular use case