I've been using a hydrowave for several years. It's another tool that can help, but it's not magic.
If the fish are shut down and negative, it won't help. If the fish just need a nudge to get into feeding mode, it can attract them and get them going.
On many days with a very slow bite I have seen it turn on after about 10 -15 minutes of hydrowave use.
Other days, I couldn't buy a bite with a dollar bill and the hydrowave made no difefrence. If they're really shut down, it's time for a cold beverage instead.