Secondary indexes - response (3) by Prem

How is the table size? Frequency of insert to the table?...If this is a small table table size (or) frequency of insert doesn't matter much for this issue.
From the above sentences I can say you are running a reporting query. 
It is definitely will decrease the perform of a insert as it simulatenously has to rebuild the NUSI table.
Instead you can first collecting statistics on the joining columns before implementing NUSI/USI.
Hope this helps!!!