Bernard--I was just thinking of my fav whistle, which is my Susato! TIA--absolutely both YES & NO!! When faced with such dilemmas, there will always be those who passionatly debate the pros & cons of a thing, & truths are to be found in both arguements. I have found that if the instrument is a good one, the artist talented, the performance is usually good & enjoyed by listeners. In these modern times we may find ourselves in many performance situations & venues, some humid or rainy or bone-dry, cold or hot, indoor & out--therefore it is logical that we look to the makers of a variety of instruments to meet our individual needs. If you find a good "plastic" or polymer instrument which plays & sounds good, while allowing you to maintain fine performances no matter the venue, say: "GO FOR IT, BABY!"
If you haven't been there yet, check out the tin whistle & flute players home in cyberspace. You will find links to whistles & flutes of all kinds & prices, as well as reviews & much debate about your question, too. (sorry, the blue clicky thing wouldn't work for me
here's the url:
          http:www.chiffandfipple.com