As a counter-perspective to recently expressed negative subjective opinions on this DAC's treatment of transients and such, I can that at least personally, I find the Bartok's rendering of leading edges to be very compelling, and is one of the qualities that sold me on the Bartok upon auditioning it.
I hear more nuance through all phases of the "sound envelope" of a note played by acoustic instrument (eg, piano or percussion), where makes it sound extra tactile and realistic to my ears. I find it very satisfying, and is a characteristic I place a lot of value in.
In contrast, I feel like some DACs (and amps!) create the impression of excitement by way of blurring of transients, whereby notes can appear quickly but without nuance to their leading edges, as if the attack phase of the sound envelope is like a simplified linear, fast-rising slope, or almost a vertical. Anyway, that's how I visualize it.
Beyond that, I don't find the Bartok to sound polite (much less "DULL") in the slightest. I do find it to sound smooth -- and very much in the positive way that term is used -- while being at least as resolving as any previous points of reference I've had experience with (namely, the DAVE, which I owned for 2-3 years, and at least one year too long). I haven't made it a mission to audition every high-end DAC on the market, though admittedly, that sounds like a frickin lot of fun

.
As always though, the only way to reliably navigate conflicting subjective opinions on such matters is through forming your own by way of direct experience.