I’m firmly in the camp of saying they are great if you have carpet and want your speaker to be stable. Ideally, the spikes can be individually adjusted so you can have them level without any tipping or rocking/unevenness.
The key thing in this situation is you need to punch all the way through the carpeting and have the spikes directly on the floorboard.
For those that claim spikes decouple: this is wrong. They do exactly the opposite
Regardless, I like the look of nice outriggers, and use them in a very unique manner:
I have platforms for my speakers and subs mounted with outriggers, punched through the carpeting as described above, then I have isolation feet separating the speaker from the platform.
For me, this is largely because my floor is super spongy like a trampoline and vibrations conduct very easily through my floor. This two part system really does help minimize the transference of vibration.
However, this is something I think is also unique to my situation and isn’t necessarily going to translate to everybody.
For solid flooring, rubber feet or isolation feet are probably best.