A whistle is a whistle is a whistle, I guess. Plus points on this one:
-it's loud -it comes with a lanyard to sling round your neck or attach to a rucksack strap -it seems well constructed/designed and unlikely to block or freeze up
Minus points:
-the lanyard is a pain if you don't want it. If you don't want it, why pay for it? -the whistle is quite pricey [I find Lifesystems' stuff tends to be].
So- if you need the lanyard and want a basic no-nonsense whistle, you won't go far wrong with this one.