I have read from folks who used both machines that the higher wattage Ultrasonic worked far better.
I know there is still very positive effect with the weaker unit as well, so it still has value if that's all you have.
I have the stronger unit, and since making this is a process, I want it to be as efficient as possible and the finished product to be as potent as possible. IOW I'm glad I have the stronger unit.
One thing, I do suggest you read through the above posts and make it with *Sodium Ascorbate* (Ascorbic Acid + Baking Soda).
Otherwise, it's a pretty acid brew when made with the Ascorbic only.