I have had these headphones in my possession for a few days now, purchased on sale for 77€ in metallic gray color. It is the first OnePlus product I have bought for personal use, fully appreciating the company.
The first earbuds I got were 4 years ago, the Liberty Air by Anker (now Soundcore), mainly for listening to music and multimedia rather than calls. I used them until recently, but their battery performance had definitely decreased and their sound was not at the same level as when I first got them.
Two years ago I got the Airpods Pro. Very good headphones for music and also a good microphone for calls. Overall, very good in terms of connectivity, with a very good transparency mode and noise cancellation. Flawless experience after two years, still working after drops in water and on the ground.
However, I wanted a second set of wireless earbuds as a backup, replacing the Anker ones, and more dedicated to music through an app. From the first contacts I have had, they have very good, powerful, and clear sound, and compared to the Airpods Pro, they have the advantage. They have customization options through a mobile application. Extremely convenient feature where you can adjust the volume with a slide up/down, something that the first generation Airpods Pro do not have. They fit extremely well and because they have the same design as the Airpods Pro, they suit me perfectly. Calls are great. They also have the ability to connect simultaneously to 2 devices and when one is paused, sound plays from the other and vice versa. They also have the feature where if you take one out it pauses and if you put it back in, the playback continues. They have more battery life than the Airpods Pro (which after 2 years still hold the same).
The negatives I have noticed so far are mainly related to the PC, where it takes 2-3 seconds when starting to play a video or a song in an app to hear the sound. For example, on YouTube through the browser it does this, and when skipping a part of the video. In the Spotify app, it only does it the first time music starts playing, not again. This may be improved in some way but I have not checked. Everything is fine on the mobile.
The second "negative" is the ANC and Transparency feature which, while satisfactory, is not at the level of the Airpods Pro, let alone Bose and Sony versions. Of course, these devices are 3-4 times the price of the OnePlus Buds Z, so it is "unfair" to make comparisons, so it is more of an observation rather than a negative.
In conclusion, for me, this is an excellent device considering the money they ask for. They have very good sound, features, an app for customization, very good battery life, and an excellent app that does not tire even after prolonged use. Personally, I highly recommend them, especially if you find them for under 100€, because they are very good overall headphones for what they offer and do not have any notable flaws in the requirements one has for everyday and hassle-free use.
Note:
Regarding the delay in the start of the sound, I used the "game mode" option available through the app and it seems to help. The sound does not delay to start on YouTube, Spotify, Discord, etc.
Perhaps this feature is for battery saving reasons and with the "game mode" activated, it eliminates the problem.