Not familiar with the Jet, but I just bought a bunch of the Fox 40s as a favor for another CPFer out of the states and they're plenty loud. They claim 122 dB, louder than the larger Fox 40 Classic. I decided to get several myself as gifts, especially for my female family.
I was going to get them from CC with some other items, but the other items fell through, so I looked for them elsewhere for cheaper shipping and found them at Fox International in a two pack for $4.00 per whistle (7.95 / 2) in high vis yellow. They only have a short poly lanyard instead of a full lanyard which I didn't care about b/c I got some bead chain instead for use on a key chain. They weigh nothing and are a pretty slim profile.
Next time I order a SL 4AA Lux from Fox, I'll probably get another package or two. They're great little gifts and very thoughtful for those that you care about - could save a life or thwart a bad situation.
If you look for them, they're called Fox 40 Rescue Howler in a two pack. I did see them at ****'s locally for $10 or $12 a pack. I'm guessing that many boating/marine shops would carry them, too.