The Fox40s are durable and reliable. I have both the regular and mini styles. Good whistles, though I wish the pitch was lower.

The Storm is big, but holy cow is it loud. While it's bulky, there's no noticeable weight penalty. I have carried it in cargo pant pockets and it didn't bother me at all.

For some reason, my hounds seem to ignore the Fox40s but respond to Storms and those 3-chamber flat boating whistles. Why I cannot say, but I suspect it's the lower pitch.

I also have the smaller version of the Storm but can't comment since I haven't really used it.

If you can afford the space, a Storm will serve well. And there's no reason you can't have a Fox40 mini with you as well.