3:00 - "including import statements".. hmm, that didn't work in beta. Will definitely try it tomorrow!

You say it's the simplest relationship, but how do you enforce it? What if I write the same user-id into two different profile records? In this regard, HasMany and its BelongsTo companion are simpler to implement, because they don't promise to much ;)

with unique(), the first item it stumbled upon will remain. BUT, this is not common for all the methods. In keyBy(), for example, the last item will replace anything before

$coll = [
    ['tag' => 1, 'value' => 11],
    ['tag' => 1, 'value' => 12],
    ['tag' => 2, 'value' => 21],
    ['tag' => 2, 'value' => 22],
];

[
    'unique' => collect($coll)->unique('tag')->pluck('value')->all(),
    // BUT!
    'keyBy' => collect($coll)->keyBy('tag')->pluck('value')->all(),
];

// output:
[
    "unique" => [11, 21],
    "keyBy" => [12, 22],
  ]