Sum Child Records with help of Slice vs Ref_rows Virtual Column efficiency

I have a parent slice which has a Virtual Column and other table columns to sum child records. Initially I used the following formula:

SUM(SELECT(Childs[Column to be Summed]),[_THISROW].[ID]=[Parent ID])

where Child is the slice containing all Child Entries.

After some reading up on the community I understood that the above might not be as efficient and
then I changed it to the formula SUM([Related Child Records][Column to be summed])

Now the issue with the first formula was that it was slowing down the app as a whole and even making the ui buggy at times as I have used a lot of CONTEXT(ViewType) to show / hide columns.
But the issue with the second option is that the calculations do not happen right away on child records in form view so after adding a child to a parent i had to add an update trigger column so the calculations get updated in form.

My question is that is this issue I am facing with summing child records via ref_row a bug?

And secondly generally which option is more efficient between the 2?

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