GoM is what started me off when I first went into magick, along with Donald Michael Kraig. I have a very fond set of memories when it comes to the GoM books and they delivered a lot of results for me in terms of practical magick. The books I mainly used are:
Demons of Magick
Archangels of Magick
Angels of Alchemy
The word of power books
Magickal Attack
Magickal Protection
Wealth Magick
Magickal Riches
Of course, I have more, but these are the ones I have used more than once. The most results I have had are with Demons of Magick, Angels of Alchemy, and Archangels of Magick. As for results, there are a lot to count, but it ranges from stuff like finding $20 on the ground one day to being able to manifest jobs and higher income flows. So a lot of results when done properly with good intention and good action in the world. Of course, I always tried to align the magick to things that were in my sphere of influence, so that helps. Hope this answered your question on results.
As for practice, I mostly use the books for practical results. These days I am using Magickal Protection for banishing and specific protections, and I have had a lot of success there for that. Otherwise, these books are my go to books for practical magick. But for spiritual purposes, I find GoM lacking in specific practices. As you know, a lot of their appeal comes from being practical and being useful for material life, which they are great for. And when it comes to giving advice on how to get practical magick working for you, they give some amazing tidbits for how to focus intention and for how magical manifestation works. But again for spiritual practices, they lack explanations for the more theoretical sides of magick and mysticism. For this, I use Initiation into Hermetics as my main path and honestly, IIH actually compliments and explains a lot of things in GoM for me if you look behind the scenes of their rituals.
On one final note, I do want to note one final thing that the GoM books are amazing for if you keep an open mind. A lot of the more traditional magick folks like to look down on the GoM rituals and say that they are too simple or watered down and hence will never work. My experience and the experience of so many other folks who use these books contradicts this idea on every level; the magick does work. And do you know why it works? It is because many of these books are based on actual historical magical traditions that have existed in the past, including grimoires and Kabbalistic magick. The GoM books took the rituals and practices of these traditions and simplified them with some chaos-magick thinking, giving the final simplified ritual practices we see in the book. But never think that these rituals are made-up, they are based on very real traditions with real power. And we need to remember that their sources are more varied than a lot of traditional ceremonial magick works in some ways. Some of their prime sources are practical Kabbalah texts such as "Shorshei-ha shemot" and "Brit Menuchah", which are definitely not sources used in ceremonial magick that I know of (think Golden Dawn). You can also look into the books by Jacobus Swart to see how some of these magical techniques are found in their primary sources and gain an understanding on how the GoM adapted the techniques into simpler rituals. This will give you a great understanding in how you could create your own rituals if you ever wanted to.
Additionally, the techniques they use are quite unique and can readily be incorporated into other magical rituals. For traditional solomonic evocations, I used the evocation keys and some words of power from "Demons of Magick" and I found they enhanced the ritual. They have a lot of good stuff in there that you can take out and use in your own rituals, even though the theory is a bit scant.
So overall, I have a very positive view on the GoM books and I continually use them to great effect in my life. I think they could be a little less gate keeping on their sources (ie "we have this private text that gives this secret technique") and be upfront on what sources they use in order to justify their claims a bit, but overall their work is legitimate. The workings are based on legitimate magical traditions from older sources and they were kind enough to condense it into simple effective rituals for us. I think they did us a real solid there, especially with the accessible prices of their books.
