If the above special features list is complete, then in comparison to the US Shout Factory release Species is missing 2 featurettes, 1 old that was present on previous BDs everywhere, and 1 new one, exclusive to Shout (H.R Giger at Work, and Engineering Life), as well as three sets of production and creature stills galleries, but has a third, new commentary from critics.
US CE is on 2 discs.
Species II only missing a stills galery, or maybe it's just not listed.
Interview with Natasha Henstridge is the same, so it would be stupid of them to include on both discs (Shout first released the sequels under their Scream label, and the Collector's Edition of the original film later, and added that interview there as well).
Species 3 isn't missing anything and has a new commentary with the journalists, and something called "Falling Apart".
Species 4 also has a new commentary, and, it seems, deleted scenes and a trailer, which are not listed on the back of the Scream Factory cover (I haven't opened it still), and is not missing anything.
Since all the sequels were only released in US and are long OOP, they're being sold for crazy 100s of dollars, especially Species 2. So it might be a good time, before everyone caught on about a UK release, to sell those.
I'll keep Species 2 disc, since it has those galleries, and won't bother for $50 with the double feature 3&4 release (seems prices already started falling).