It's fantastic!
There was an immediate difference in my dog's behaviour.
He responds to it calmly and it doesn't disturb him in any visible way - in fact, he enjoys our walks now more than ever before!
The only thing I will say is that the prongs sometimes get caught in the centre plate and so do not align properly.
This takes some fiddling to correct before using on the walk.
Other than that, we are very pleased.