This is a very good book for learners (like myself) with many examples of usage and idioms. However there are some notable omissions. The grammar section is an aide-memoire, not a textbook substitute.
A useful feature of most dictionaries is that every translated word offered in one direction should also appear in the other direction. Often, when you look up the suggested word, it has a meaning subtly different to what you had intended. This dictionary often offers a word in the English/Welsh section, which has no entry in the Welsh/English section.
For example, missing in the Welsh/English section are "amaeth (agriculture)" and "amaethwr (farmer)". Ffermwr (farmer) does appear in both sections, but amaethyddyaeth is given as a translation of agriculture, only appearing in the English/Welsh section.
This dictionary is very useful, but you will also need a more comprehensive dictionary to fill the gaps in this one's vocabulary.