I have been using the A4 as my daily driver and main iem since launch but that has changed since the A5 arrived. I have replaced the A4, not because A5 is newer shinier etc, but I feel the A5 greatly improve upon the A4 in some key areas.
The greatest improvement, imo, is in terms of ergonomics and comfort. The A5s just positively disappear after putting them on. Funny enough I have been using the A5 with the a4 cable because it lacks the flexible earhook and is softer, producing less noise. The a4 cable helps the A5 sit easier in the concha as well.
Second - the sound; The A5 has a meatier midrange as compared to the A4, which I feel is thinner in comparison. The A5 produces a denser and thicker sound with more detail and bass. They have improved the detail and resolution, while also making the sound more "musical." The end result is an iem which is enjoyable to use all day for any application. Heck I have already done some guitar monitoring with the A5 and I am happy with the timbre and how realistic instruments sound.
The A5 has that magic sauce that made the A2 legendary. YMMV but I feel that LZ has done a great job in all departments, not just sound.
BUT I still dislike teh stock cable and lack of accessories.
Edit:
@SteveKiwi Ignore my last tag - had a brain fart, meant to address someone else lol