Warthur
In Porcupine Tree's discography, Insignificance is to Signify as Staircase Infinities is to Up the Downstair and Yellow Hedgerow Dreamscape is to On the Sunday of Life: a companion piece compiling various songs which didn't make the cut for the parent album.
That said, the approach is somewhat different this time. Compared to Staircase Infinities and Yellow Hedgerow Dreamscape, you get less entirely original songs and improvisations here and more in the way of alternate takes and demos of material which were incorporated into Signify.
There's still some entirely new stuff here, like the two takes on Wake As Gun or the funk-tinged Neural Rust, and both these unique songs and the alternate versions of Signify material tend towards a somewhat more mellow and psychedelic-tinged take on the overall approach of Signify than the harder-edged version we got on the main album. If you like Porcupine Tree's pre-Signify material, then you may well enjoy this; if you think Porcupine Tree didn't get good until Signify, you might find this inferior. And if you don't actually like Signify itself, why are you even considering this?