As good as those driver are, I'd still take the planar magnetic drivers from BG in an open baffle configuration over them in a flash.
Interestingly enough, I have been able do that exact comparison.
I have a set of the Seas C18s in my living room system running in an open baffle with a passive crossover between tweeter and mids, and an active xover to sealed boundary woofers at 250Hz (a bit like Lyngdorf speakers).
I also have a BG Neo10 and Neo3 based full range fully active full dipole system (with Peerless SLS10 woofers) in a dedicated room downstairs.
Naturally, in the interests of science, I built a baffle for the Neo10s and Neo3s and hooked them up for a direct comparison to the Seas coax system. I tried them both with passive crossovers like the coaxes, and fully active. Xover was 4K passive and 3K active.
The BGs are dipole all the way up, the Seas is open baffle, but obviously not dipole above the crossover point.
The baffle I built for the BGs was a tapered one to maintain dipoleness as high as possible.
Both systems sound very good.
I agree with the comments here that the Neo10 is close to being top of the heap for midranges. It is certainly top of the heap for dipole midranges. I'm not as convinced with the Neo3 dipole, but it still sounds awfully nice.
The Seas C18 (as you'd expect for the price) is also pretty darn good. The woofer is of similar quality to Seas W22 I used to have in my Orions, and the tweeter remarkably good for a coax.
In pure sound quality terms I would give the edge to the BG combo. A bit clearer and I just like the sound of dipole tweeters.
However, the Seas was close, and notably better in coherence and soundstaging. The trick, I'm sure, is the superb horizontal and vertical dispersion.
The room they are in is dedicated to looks not sound. As a result the Seas are too far apart, mounted too high, too separated from the woofers and too close to a wall.
Yet they sound good everywhere you sit. Or in my case slump.
When fully reclined on the lounge, the tweeters are about a metre above my ears.
So for ultimate sound quality, the BGs are a bit better if you are prepared to fit in with their strengths. But the Seas coax sound better (in this room) in more places.

