Are there any risks or disadvantages?
Sometimes, when it is very bright outside during the exercise, the eyes may get some tears. This may be a problem for women with make-up. After a few months this annoying effect will stop. I do not know any other negative side effects. But the ultimate decision and responsibility whether, how, when and how often you want to do the exercise is up to you.
Regardlessly of whether you do the eye exercises or not, it makes sense, to visite an ophthalmologist regularly. There are several reasons, why the vision of your eyes may get worse, and not all can be improved by eye exercise.
In the darkness or in dark spaces - such as in a disco or bar - the vision is far worse than during the day. The darkness let your eyes open the pupil in order to let more light in, and the depth of field gets reduced.
This physical phenomenon is similar to the effect in a foto camera. But after some months of practicing, you will be able to see sharply also under weaker light conditions.
Even if short-term vision improved significantly, it takes months, often years before you see as good without glasses as with glasses. So do not expect miracles overnight. Otherwise, the exercises are easy to do and they will not take a lot of time. You can do them while waiting on the bus, train etc. You only have to remember to do so.