Nothing wrong with using the Epic coupons to get the game a bit cheaper.
The 2 clients thing is a bit unfortunate though. Other clients like Steam starting a UPlay client so it's not a new thing or specific to Origin or Epic. It is what happens when it's the same companies that make the games also decides to sell them.
When a game is from a publisher who has its own launcher (EA, UbiSoft, Bethesda, Rockstar, ActivisionBlizzard), I always check first if that launcher must be used. At least on steam that information is given in the description ("EA on-line activation and Origin client software installation and background use required").
For most EA games (and I think all UbiSoft games?) on steam you still have to use Origin (or Uplay) when running it, so I buy them directly on Origin/Uplay (or via an official retailer like humble, gmg, fanatical, etc.; not to be confused with keystores like g2a who damage the developers with dumping prices, and where the origin of the keys is often dubious at best) to avoid that.
The only exeptions for EA I found thus for are SW: Squadrons and Command & Conquer Remastered, which only need you to link your accounts once, but don't force two launchers on you. Does the Epic store not tell you about the Origin launcher? Regardless of that I wouldn't buy anything from the Epic store anyway. Their agenda of game exclusivity should not be rewarded and the launcher client itself is still barely functionial in comparison to their competitors.
