Zvezda sell both their own models as well as Heller reissues.
While their own models are generally sound from a modelling point of view, they all suffer to various degrees from faulty research.
As Millard already noted, their ancient ship range is little more than a collection of Hollywoodesque movie props (not helped by Zvezda using the same basic kit for a 480BC, two 260BC and a 50AD warship). As far as the Roman Punic war warship is concerned, that's probably not too much of a problem, as we know little enough about how these looked in the first place. The "Greek Trireme" however is a more serious case of sloppy research, as we have a - not 100% accurate, but pretty close - reconstruction afloat, which would have been easy to study.
The Zvezda cog is an interesting kit and much more accurate than the ancient, well, craft; the two main issues here are the scale, which is more around 1/65 to 1/60, and the deck, which is dead wrong, the planks all going from bow to stern, while they should go from one side to the other. Again hardly to understand as there's one in fairly good shape in Bremen which is well-documented.
The "Crusaders' ship" or whatever it is called is simply a cog with some additional parts. The same comments apply - and of course it's not that appropriate for crusaders...
In all I'd say the cogs are the pick of the bunch, particularly as the Heller reissues I've seen aren't those of Heller's best efforts.
Jorit