Having an open mind is key.
I do not think what I use for fleas, is considered holistic in the least. However, our homeopathic vet recommends neem as it is extremely safe, that recommendation coming without selling me any of the products. So it is nice to know that neem does not interfere with their system and is safe to use while treating with a homeopathic remedy.
There are many safe (non-pesticide) flea preventives. It does take some research to find those, and I have heard of that pendant. It looked enticing, and too good to be true. I am not surprised it worked for your dog, I had heard good reports on that. I tempted when I looked at that pendant, but my dogs are oh so exposed and we are very active (hiking) with them and their doggy friends.
I decide to go with a natural Neem pet concentrate, and have been impressed with that. The small bottle mixes up over a year of applications. We have not found a flea/tick yet on our dogs, and they hike and roll around in the mountains, sometimes with other dogs which we found to have fleas after the fact. None of those fleas found ours appealing, so this must be working.