Sorry if I didn't explain things well enough. The synergy with Ahri's skills, mobility and muramana makes the item very cost effective on her, to the point where it becomes an arguably optimal item to build, either finished as a first or second item (such as stacking tear while building echo/glp). The damage also makes her incredibly hard to negate as she is doing physical, magic and pure, as well as being higher single-target burst in the mid game than full AP. There is also the potential to completely play towards physical damage, either as a pseudo physical assassin or completely as an ADC. I have played numerous games in both normal and ranked(Gold) experimenting in both AP/hybrid and ADC with some good results. I also highly suspect with the changes to manamune in the next season, she could be very interesting to play in that style.

Incase it wasn't clear in the discussion part of muramana, the item provides about 700 damage to your burst through shock and AD (aa), whereas seraph's embrace at the same mana would provide 69 AP. With a total AP ratio of around 327% (including E bonus and hextech) you would gain 226 magic damage in your full combo. Of course seraph's embrace also offers a shield for the lesser damage, and can be boosted further with deathcap for 134 AP (438 added magic damage). I hope this clears some things up!

Glad to hear, I will most definitely keep developing the build and guide, if there's any areas you would like expanded upon specifically, please let me know!

Thank you very much! There are very much similarities in this playstyle and possible builds so well spotted! I would say the major difference are the easability of harass in lane with Q & W, additional cc for both yourself and your support, extra sustain in lane from Q, and dare say more mobility (albeit for a briefer period of time) during fights, chases and escapes. Also once you land charm it's kind of over unless they have a form of cleanse.