Samyang, Bower, and Rokinon, are all the same. Not sure why they choose to break out into 3 different brands. There may be slight cosmetic differences between the brands, but the elements, groupings are the same.
As already mentioned the 14mm was a huge surprise when it came out, being a very very sharp lens even wide open. I have used the Bower version on Canon's 6D and Nikon's D800e, you will see just a bit of corner fall off on the D800, but on the Canon sharp full frame. There are some distortion issues but most can be easily corrected. The 14mm is not filter friendly and I don't know of any 3rd party solution for it.
The 24mm 1.4 is another wonder lens, and from my outdoor and night work, it far exceeds the highly vaunted Nikon 24mm 1.4, the later have huge coma distortion issues until around F2.8 or 3.2. The 24 is an excellent lens on my D800 or Canon 6D, remember you can easily adapt the Nikkor version to Canon but not vise versa as you will loose infinity focus due to focal flange distance.
The 24mm TS-E did not get the same great reception as the others. I have not used it after what I read about it's performance. However it's still on my long term list as it seems to still outperform the Nikon 24mm TS-E by F11. I tried 3 of the Nikon's and never found one that was that good shifted. Many love the Nikon 24mm TS-E and I am sure there are sample variations.
One thing, the warranty on the Samyang, Rokinon, Bower lenses is nothing like the Nikon or Canon, Sigma etc. They have a U.S. number, and you have a 1 year warranty, policy is not however to repair, but instead you send in yours, they verify it's not working and send you a factory refurbished lens. This has happened to 2 separate photographers I work with on the 14mm.
Also, they are all Manual focus lenses.