I've been working with George Protos (PointingOut Way) for a while now and he has been very good in pointing out the One Taste state/level in Mahamudra. I'm now going to take a stab at describing this.
Just as the no self meditation in Mahamudra helps us realize that the self is a construct and the yoga of unelaboration demonstrates that the world is a construct (and that spacetime is a concept), One Taste shows that a separate awareness is a construct and that awareness/phenomena is simultaneous.
To some extent this is obvious. If emptiness of phenomena shows that phenomena are constructs and emptiness of self shows that the self is a construct, then it's natural to affirm awareness and phenomena as co-present since you cannot have one without the other. However one has to be extremely careful unpacking this state as other traditions like Theravada tend to focus on phenomena only (via the dissolution experience) while Vedanta tends to affirm the pure consciousness event in which no phenomena are present. Mahamudra then sits in the middle (with the metaphor of being the flashlight and not the person carrying it or the illuminated content) adopting a post-tantric non-dual stance. It also refuses to conceptualize this state except to carefully point out a simultaneousness of awareness and content without reifying each one as a separate entity.
It is important to understand the gains stemming from maintaining One Taste. There's an automatic emptiness wherein anything that arises is not elaborated but tagged as empty upon arising. The impact is that things tend to get taken care of immediately with high energy and without as much attachment (so you do have to be careful doing this in public since taboos could get broken very easily). There's also a brightness and clarity to events as if they are self-illuminated [which makes sense since every event is also simultaneously tagged with awareness and perhaps parodied as "I see god in everything" :-)].
Once again Tashi Namgyal:
"[T]he meditator realizes [that] the awareness of one flavor manifests itself in diverse forms and how these appearances and existences are of one flavor in primordial evenness. The meditator has achieved insight into the essential nature of one flavor when he discovers the intrinsic identity of every appearance as a self-manifesting objectlessness and evenness in its primordial nature."
