I used Samyang cine primes on many occasions, mostly on Red and FS5, FS7 etc and need to say I would compare them to Canon Cine Primes easily, for 1/10 of the price. They are also much lighter.
I have a dislike to CP2 and only use them under duress from production for very clean documentary gigs, with 1/8 BPM anyway - they have annoying tendency to milk as well with the flare, and too sharp rendering when there is non.
Perhaps worth mentioning we use a lot of NIKON ais in UK for more creative pieces, and im a big fan of my set - would love to get them rehoused one day.
I normally insist to get Zeiss super speeds Mk2 on most of my spherical commercial work - perhaps closer to Samyang's in my opinion than Zeiss CP 2s.