There were times that I was wishing that I never left my Sindt at home.
I think you will find your Sindt is heard just about as well. I remember playing one night, perhaps fifteen years ago, thinking I was playing away unnoticed when Marion McCarthy who was sitting opposite remarked on the lovely sound of the whistle. I was mortified. I let her play a tune and was amazed at how clear the whistle sounded among the fiddles, flute and concertnas and whatever else was there on the night.
I don’t know about switching from Sindt to Killarney. I have both and yet I’ve found that I prefer certain tunes played better or easier on particular whistles. I enjoy wooden whistles vs. metal for several of my tune repertoire which isn’t very big, although I’m not a professional performer either.
Yes, I’ve heard the same about Sindt whistles Mr. G. I’ve gone to the bathrooms of session pubs and have been amazed/disturbed 
at how clear the other Sindt players come through. Brought both out last night. Another Sindt player noticed the difference, especially the volume and brightness. I’ll prolly keep the Killarney as a novelty or car whistle but I have 20+ years playing the same whistle…we have been through a lot together and I have a lot of memories created with my Sindt. For example, as I explained my reasoning to friends last night, the Killarney has not been played solo by me, while being backed by Canada’s National Philharmonic Orchestra. The Sindt has 
It would be like giving up on an old and dear friend. The differences are not that substantial to do such a thing. Plus, I like being “hidden” in the background. Sindt player for life here. Ashamed of myself for ever considering otherwise