My introduction to Nirvana (UK) as they are now known (after a settlement with the more famous Seattle band over use of the name) through their excellent single "Rainbow chaser". The track was included on the Island sampler "You can all join in". With it's phasing and orchestrated keyboard sounds, it was way ahead of its time (1968 I think?).
Most of the band's output around that time was softer more traditional pop, such as "Penticost hotel" and the delicate "Tiny goddess". The band were essentially a duo of Patrick Campbell-Lyons and Alex Spyropoulos with supporting musicians as required. Event heir album tracks were seldom more than 3 to four minutes, so the prog link is somewhat tenuous.
I loved the cover of the "All of us" album (full title "The existence of chance is everything and nothing while the greatest achivement is the living of life, and so say ALL OF US".
It was only when Campbell-Lyons released "Local Anaesthetic" under the Nirvana name (but a solo project) that I felt he dabbled a bit with prog, but the results were somewhat dull and ininspired. I also held against him the fact that he destroyed the great "Rainbow chaser" with his reworking on "Songs of love and praise".
The best thing to happen to the band in recent years was Cobain's use of the name. It rekindled interest in their work, and brought them the press interest they had never achieved when they really wanted it.