Nuvista Tubes - General


May I have opinions please on the pluses and minuses of Nuvista tubes versus vacuum tubes? Supposedly and from the basic homework I've done, Nuvista tubes purportedly offer high reliability, low microphony, low noise, consistency, and small size compared to their vacuum counterparts. So what's the down side? 
128x128gdhal
@viridian 

Do you have an opinion (and care to share) of the Musical Fidelity amplifier products/designs that use nuvistor tubes? I'm currently using an M6si which I'm very happy with, but the "nuvista" series is their top-of-the-line offering. Thanks.
Post removed 
Post removed 
To clarify one other thing, Nuvistors are vacuum tubes.
Appreciate the clarification. Then, given they are vacuum tubes, assuming all else being equal, should one expect to achieve the same level of "famed" tube sound by using nuvistors (as compared to some other vacuum tube)?