These products tend to get mixed reviews which reflects I guess their relative success.
We have used these (or equivalent) products for 5 years now replacing them as and when they get broken.
Our experience has been that they are an effective and maintenance free remedy if properly used. To use them properly requires two things.
First, contrary to product claims, we have never found that these will remove or drive moles away from a patch in which they are already established.If you have a mole infestation then you have to catch or destroy the creatures first by some other means and then utilise these as preventative treatment.
Secondly, a single sounder alone will not work. You will need at least two and in preference three or more effectively to police an area spaced and overlapping so that they are working together zonally rather than alone.
Generally if that approach is used we have found them very effective in preventing further infestation and the solar cell is more than worth the added expense over battery powered models. In an area of relatively high mole infestation, the one garden we use these in has been free of moles now for 4 years.
Yes they do make a noise intermittently, but it is not overly intrusive and is more than outweighed by the benefit achieved.