Side note:

It's not often worth persisted expressions like this - this optimiser very frequently chooses to recalculate the value from the base columns instead - particularly if the computed value is part of a useful index, and the base columns are.

Not a huge consideration here, given the size of the persisted data and the complexity of the expression.

For complex or otherwise expensive expressions, consider indexing the computed column without persisting it (or adding it as an INCLUDEd column on an existing index). It surprises some people that you can (very often) index a non-persisted computed column, but it is true.