First, let me preface by saying that there have been - and presently are - important Rabbis who have rejected various parts of Kabbalah, often large parts of it, as well as some of the more popular interpretations of Kabbalic works, especially, it seems, the work of the Arizal (examples include the Vilna Gaon, who rejected the Hassidic understanding of Kabbalah, quite fervently; Saadia Gaon who, at the least, rejected the idea of reincarnation as being non-Jewish; Maimonides who, at least, rejected the extreme anthropomorphism in many mystical Jewish writings, among other issues; Meir ben Simon who essentially accused many contemporary Kabbalists of preaching heresy; Yaakov Emden who created a detailed critique of the Zohar, accusing it of heresy; Leone di Modena who rejected the Sefirot precisely because there would then be no problem with Trinitarian theology, in his opinion; Abraham ben Moses ben Maimon - the son of Maimonides - who fervently rejected the idea that time and space in any way apply to God, thus rejecting the panenthism present in much of Kabbalah; Yihyah Qafih who rejected the Arizal more or less wholesale; and, most notably amongst present-day Rabbis, Ovadia Yosef who was, for a time, the Sephardi Chief Rabbi of Israel, though he is actually a Mizrahi Jew, and holds an exceptionally high status in most Mizrahi communities). Now, onto the actual article.
A major problem with this article is that it compares the Sefirot to the Trinity. In Kabbalah, properly understood, according to most Kabbalists, the Sefirot are aspects of, or emanations from, God. In true Christianity, the Trinity are not aspects of, nor emanations from, some singular person. The Father, the Son, and the Holy Spirit are three distinct persons. In the early Church, the question was never "OK, we know we have one God, so how is He three persons?" but rather "OK, we know we have three persons, how are they one God?" This distinction in emphasis is extremely important because it underlies something that is difficult to express, but nonetheless Christian doctrine. The article claims that the Sefirot are a compound unity comprising God. This is inaccurate. Rather, they are the way He works in the world, much like the energies of God, found in Christian writings. They do not comprise God, rather, they emanate from Him. While some Christians will say that this is no different than the Trinity, us Orthodox call those Christians heretics.
They even quote 1 Chronicles 29:11 in support of their idea "Yours, O God, are the Greatness (Gedulah), the Power (Gevurah), and the Glory (Tiferet), the Victory (Netzach), and the Splendor (Hod), for all that is in heaven and earth (Yesod), Yours O God is the Kingdom (Malkuth)." However, if properly understood, no one could claim this is support for a Trinitarian God. Rather, it is support only for a God that can, in some sense, be known. If I say that Alexander is intelligent, funny, and athletic, am I claiming that he is a compound unity and that those three aspects are in some way independent of him? Of course not. Rather, I am describing him, not diagnosing him with DID.
The author of the article also writes that "kabbalists recognize multiple "grades," "degrees" or "beings" in the Godhead," and says this isn't different from three persons of God. Clearly, this author is not a real Trinitarian Christian.
As well, the author seems not to understand the idea of the Incarnation of Christ very well, seeing as how he presumes that the belief that the Shekhinah can appear in an anthropomorphic shape, such as the burning bush that Moses interacted with. This is extremely different from the idea that the Son of God BECAME a man, He did not merely put on flesh as one would a costume, but in every sense became a man. If the author of this article believes that these are still similar in any important way, he must believe that Kabbalists think God became, truly, a plant.
The author is also selective in his speaking about Metatron. While it may be possible that some Kabbalists believe Metatron is in some sense God, virtually all of them - instead - believe he is Enoch. In fact, when the Talmud records Acher entering Paradise and seeing Metatron seated, he assumed Metatron was God and became a heretic by declaring that there were two powers in heaven. In fact, according to the Talmud, Metatron received 60 lashes from God as proof that he could not be God.
This author is either: 1.) Uninformed about true Christian theology; 2.) uninformed about the Kabbalah; 3.) or, more likely, uninformed about true Christian theology and intentionally misrepresenting Kabbalah.