Though it is a great book, it is itself filled with a good amount of Mr. Flowers own personal ideas and personal fantasy. I would also recommend that you purchase The Greek Magical Papyrus in Translation by Hans Dieter Betz, The Leiden Papyrus, Ancient Egyptian Magic and Divination and The Greek Qabalah by Kieran Barry, so that you can form a balanced view of the tradition and not simply go on what Flowers says alone. Flowers does of course offer an excellent bibliography with many worthwhile titles.
I would also like to laughably dust Seavels comments off to the side, and point out that if the PGM are mere fragments of a lost tradition, than so too are the grimoires. Note that the summoning of spirits as we know the practice today is derived from practices found within this very interesting tradition of practices. Of course, they didn't quite have demonic and angelic hierarchies back then and they would quite often evoke the very deities themselves and this was done by vessel or by lamp and usually with a child medium but not always. Compare this with nearly any example of renaissance era evocation, which would use similar devices and you will see the obvious parallels between the two traditions. The Demotic papyrus refers to the practice as divination, and while that may be the purpose of performing such rituals, the act itself is clearly one of evocation.
To say that one set of practices is more powerful than the other is neither here nor there, they are both arts of antiquity and one could well argue that modern practices would be more practical or more relevant. For someone that is of a more "Pagan" persuasion, the methods of the PGM are going to be much more comfortable than many of the methods outlined in the grimoires.
Not to side track the thread much, but here I give an excellent example of "divination by vessel" from the Demotic papyrus which is clearly an act of evocation.
Place vegetable oil into the vessel and proceed as above (the instructions were to fill a vessel with oil, light a lamp and place it by the vessel and cover yourself, the vessel and the lamp with a white linen robe, a common practice herein, though it is nclear to me if you simply wear the robe, or drape everything with it, Aet)
Speak unto me, Speak unto me, Hamset, god of the gods of darkness, every demon, every shade that is in the West and the East, he that hath died hath done it (perhaps a refernce to the accomplishments carried out by the soul of Osiris after death), rise up to me, rise up to me, O Thou living soul, O thou breathing soul, may my vessel go forth, my knot here to-day, for the sake of the vessel of Isis the Great, who inqireth for her husband, who seeketh for her brother; Menash, Menash, Menanf, Menanf.
say; "Menash, Menash, Menanf, Menanf, Phoni, Phoni" a multitude of times; and you say to the boy (strange, as no reference to a medium is previously mentioned) to say; "Depart, O darkness; come to me O light," and open your eyes at once. Then the gods come in and tell thee answer to everything.
Very beautiful, simple and clearly an act of Evocation.
And on another note, does anyne know a good place to pick up washing soda these days? I can't seem to find it anywhere!