It's not quite a 4" leash to their parent model though sometimes not all that far off. They have to stay within the command distance of their parent model (6 for aquans 8 for Ryushi) and can then make attack runs up to their movement value against targets so something like Ryushi fighters could theoretically get 26" from their parent model.
Teleporting carriers can be fun using the shunt rules although there are also some potentially very unfavourable results on the shunt table e.g. your opponent getting to shoot at you as you arrive so it can be a bit risky.
Ryushi are one of the alliance factions so you can find their stats in the Alliance of Kurak pdf at
http://www.spartangames.co.uk/resources/downloads. They have some good stuff although only being one of the supporting races at the moment means they're a bit limited in the ships available compared to some of the other factions as they only have 4 and one of those you can't use in games below 800pts.
Personally I'd go for Aquans or Ryushi though I may be a bit biased as those are the two factions I run / am planning to add to my fleet.