Not having seen it, I must rely on the judgment of others. It seems his heart was in the right place and his intentions were good, but his skill as a translator? Not so much. Describing the situation, someone wrote that "Blitz's Hebrew was less than adequate and he relied heavily on translations into German, including that of Luther, often leaving his Yiddish translation resembling the German more than the Hebrew original.
In Rambaman"s introduction to the Nesivos Schalom pentateuch, the Or Le-nesivah there is a review of the Jewish Bible translations which preceded his own version, and here is what he writes1 of Blitz:
Another German (ie, Yiddish) translation by R. Yekusiel Blitz of Wittmund was also printed at Amsterdam, 5439, with haskamos and sanctions of many distinguished rabbis of that time. R. Yekusiel says in his preface that he had seen the German (Yiddish) translation of the Pentateuch printed at Konstanz, and found it so faulty and unfit that he was convinced the translation could not emanate from the celebrated German grammarian (ie, Elijah Levita). I, the writer of this have never seen the translation attributed to R. Elijah, as it cannot be found in our country, but I have seen that of R. Yekusiel, and discovered that he finds fault that he himself is guilty of. Though he may have had good intentions, and that is why the scholars of his time gave their approbations,the results of his work is not deserving of praise, because he was quite ignorant of Hebrew, and therefore could not penetrate into the depths of the Hebrew style, but what he understood he rendered into a corrupt language, so that one who has been accustomed to clear language is disgusted with it.In view of this, I was quite interested to find a review of this very Yiddish Bible in a German periodical from 1749, the Nachrichten von einer hallischen Bibliothek.
This review is preceded by a review of another judischteutsche Bibel. (pp. 95-110) Needless to say, this review is not so impressed with Blitz's feeling for pshat, to say nothing of his language, as far as I can make out.
1 Unpaginated. Haha, it is on the 26th and 27th page of the JNUL file I linked above.