Sainte Chapelle is awesome - undoubtedly one of the great sights of Europe and not to be missed. Conciergerie is less awe inspiring but still very interesting if you're prepared to read, learn and inwardly digest from all the information available. The Viator ticket represents good value. My tip: Get to Sainte Chapelle as soon after opening time as you can. I first visited Sainte Chapelle in 1978. One simply strolled in at one's convenience. How times have changed!
Not exactly what I expected, but worth the money, as it was only as small amount. Glad I did not spend a lot for the tour. The was recommended by my guide from the another tour to truly understand what Notre Dame looked liked on the inside when it was painted. The colors were amazing. It was remarkable from that aspect. The Conciergerie aspect was unremarkable. I really did not learn anything from that tour.