I treat myself once a fortnight to a massage and book one for my OH, the PWP, once a month. I suffer terribly with knotted muscles in my neck and shoulders and find that once a fortnight keeps the dreaded knots at bay. OH just finds it relaxing, I wish!
Our therapist seeks out the problem areas and sorts them out.
I may manage to use the gadget but my OH couldn't possibly manage to use it.
I would also point out that by using this gadget you are, at the same time as massaging your shoulder muscles, you are also using them to hold the thing so that they are not even relaxed in the first place.
Lying face down for a massage with no muscles actively in use allows the therapist to do their work.
If it works for you then fine but I would recommend a proper massage with someone who knows what they are doing rather than a machine for self use which may cause more harm than good.