Personally, Angels of Omnipotence (2021) is one of my go-to books for workings and I LOVE Ebuhuel in particular, who I have become close friends with. He gave me permission to make an open offer for help passing on that I posted here: Ebhuhel offer: Help to avoid reincarnation traps
I don’t have the “Secret Angel Magic” book (2023 - it came out later and I just don’t feel the need for it, I also just don’t really like GoM in general as they feel a bit.. Llewellyn, to me, if you know what I mean 
).
As it seems to build on the Angels of Omnipotence, I’d suggest getting Jareth’s Book first, getting the original contact without the 2nd authors overlay, and then the Blackthorn book can add a layer of richness perhaps. 
There must be some redditor or whatnot out there being weird about it, because one other person said that also - it’s all hearsay as far as we know so far.
On THIS forum, many of our members have worked with them, and while I don’t recall anything negative, it’s worth using the search on the specific entity names to see what people said, and if anything gives you warning vibes.
I seem to remember there was some kind of drama when the book came out with the people Jareth worked with on the original ideas, and I wonder if that’s related.
Not more than the usual - you should have your spiritual hygiene on point, know how to recognize and banish parasites that get attracted to ALL magickal effort, and set up your wards and shields. I will post this until I’m blue in the face an nobody reads it - prove me wrong…
The first thing to get under your belt are your protections: like spiritual hygiene, then you want to get into developing your astral senses and avoiding impostors and parasites
My advice, in any case, is do not listen to hearsay, dogma or other people’s drama - magick is PERSONAL, and you will only find out if it works by trying it, and then you must make up your own mind. If you are a mage and not a sheeple, your Will is what matters, and nobody else’s. The fact that you are even considering the work, means you have an open invite.
“Do as you will is the whole of the law; love is the law” - basically if you love it, do it. Do both, do either, it doesn’t matter as long as you act on your will. The more the merrier.