I have had bipole main speakers for almost 20 years now, and had Omnipolars as mains in another system five years. Both were by Mirage (RIP).
The effects of either design is pretty similar, though Mirage’s Omnipolar design had about 10 further years of research, resulting in a near point source that was omnidirctional with a balance of 60% to the front and 40% to the rear. I’m pretty sure this ratio was the result of measuring and averaging the dispersion pattern of a wide variety of instruments as well as the human voice.
And that explains why it sounds so natural and takes away typical stereo artifacts. Omnis, Bipoles, and Omnipolars throw a pattern that is similar to the soundscape of live music in most venues. The soundstage is as large as the room. And like live concerts, the soundstage doesn’t collapse just because you’re sitting to the side. With omnidirectionsals and similar variants, you can still hear the whole stereo image even if you’re positioned to the left or right of both speakers.
They eliminate dead spots and suckouts that would remind you you’re listening to speakers. You’ll also note that all MBLs are omnis and they consistently rank with Stereophile’s cost-no-object class A speakers. Since live music is generated from omnidirectional sources (voices, instruments, etc.) then I'd say that omnis capture the "real deal" in some ways that front-firing speakers cannot.
I still have my bipole Mirage M5si’s in daily use, but I replaced my OMD-15s with Magneplanar 1.7s. With some more careful placement, I was surprised how the Maggie dipoles did something very similar to the Omnis with the added benefit of automatically canceling that 100-200Hz upper bass room boom.
