Hello, considering one of these as a ‘night shift’ practice whistle, anyone have experience/opinions?
Don’t want too much volume, need something sturdy enough for rucksack
I think that’s a good choice. I used to carry a few Dixon polymer whistles with me to work for amusement during breaks. They work well in that regard - very lightweight, fairly durable, decent players, pretty good tone, no clanking around in the bag, etc. I don’t find them to be particularly loud especially the lower pitched whistles. The only downside I can comment on is that the Dixon polymer whistles can warp in high temperature such as locked in a car during the high heat of a summer’s day. If you avoid that you’ll be fine. I also carried the same Dixons backpacking and cycle touring. Good fun around the campfire in the evenings. They’ll hold up fine in the rucksack.
Feadoggie
Thanks for that sounds ideal (I based my choice on the description given on Big Whistle website) I work night shifts in a hospital, it’s either panic all night or utter tedium (never seem to get a happy medium) so I kill time by doing a little furtive whistling in an empty office. Management have no objection but I’ve had some moans about my Gen Bb.
Never thought of the warping issue thanks for the warning, it will be in a rucksack for a 20 mins walk at the start and end of shifts so it should be safe from that.
About your playing? 
Just kidding! Is the volume an issue with the Gen Bb. If so, I don’t think the Dixon is quieter. If anything it has a fuller sound. But it can be played muted with the usual contraptions.
Carey Parks has just started selling a PVC Bb which incorporates his version of a mute.
Feadoggie
I get very few complaints about my playing (as long as I play ‘Wild Rover’ endlessly 
) The upper register of the Gen irks some though. Surprised at your comments I thought the Dixon would be quieter than the Gen !!
OO that Parks does look nice, will contact Big Whistle to see if they intend stocking that (they do carry his D whistles)
Thanks again
Well, some Gens do vary a bit. I have a couple older Gen Bb’s that are just terrific top to bottom. A newer one didn’t thrill me so I made a new head.
As for controlling whistle volume, it is my experience that any whistle can be played quietly. So there is really no need to buy a new whistle unless you want a new one. Search for “mute” on the whistle board and you will find a history of posts on the subject. I cut up cross-sections of bicycle innertubes to make mine, elastic bands work too. You merely slide it over the voicing window to bring the volume down. A piece of tape works as well. Any adhesive tape in the hospital? Just cover half of the window.
You can always play using the “whisper method” as well. That’s my favorite but some players don’t like the fact that you only hear one octave of notes.
Good luck.
Feadoggie