The authors do not cite and compare our work although they try to solve the same problem. In particular they use a similar fairly innovative way for the field to treat the input data, as we and another publication did, but they cite neither of these 2 papers.
In the case of close proximity and (f)actual relevance, I do not see a problem - it is scientifically justified to provide insight and highlight overlap. I am slightly concerned, however, whether just addressing the same research question is enough. In even moderately populated (-ar) fields, it is impossible and even undesirable to cite all relevant literature, and citations along the lines of "X also does Y, period" may be seen as redundant, not supporting the paper narrative or social gestures. In such a case, unless there is an evident methodology or results link, which factually adds something to the narrative, I would think longer about suggesting a self-citation, even if the intention is perfectly benevolent. Bottom line, would it really add something, or is it one of those interchangeable citations that "must" be put in for completeness? In the case of a small area, where listing prior work is helpful to the reader, I would not hesitate.
There is an additional comment to be made about the contribution of the paper. If the contribution claims to be technical ("We found new way A to do B), I do not see a problem. If, however, the paper claims to do B which has not done before, which your paper does with a different methodology, you should definitely mention this in the comments and examine carefully if there is an actual contribution of the work you are reviewing and if it differs enough to warrant publication.