Thanks for welcome and for suggestion OldBaldGuy, Be Prepared. This whistle looks good too.

ACME Tornado Slim Line is the most accesible for me here where I live (Czech Republic) since local store carries it and in addition itīs not expensive. It exceeds S.O.L.A.S requirements. So I will probably buy it. However If it turns out that Fox or JetScream or ACR are really better I can always purchase them later. I may be wrong but I guess these small whistles performs + - equally.