I've previously tested Repente's top-end Aleena saddle and I got on well with it. The Prime, overall, is better: I found it more comfortable, it's better value and it's still very light.
Pros: Light, comfortable, RLS system allows cover changes
Cons: Expensive, cover options could be extended
The Aleena is a very, very light saddle at 130g, and you pay a handsome price for that. The Prime is over £100 cheaper but it's still impressively light at just 166g. Other similarly priced saddles we've tested recently – the Selle San Marco Mantra Full-Fit Carbon FX and the Fizik Antares R1 Versus Evo for example – are within a few grams of this Repente seat, so it's pretty much bang on the money.
The Prime is cheaper mostly because the materials used to produce it are. Instead of the full-carbon construction of the top-end saddle, the Prime uses a thermoplastic composite base. The rails are still unidirectional T700 carbon, and they're still taller than they are wide, so they won't necessarily work with seatposts that clamp side to side.