First experience with build 300 was quite rocky, but that is purely my own fault. I was working on a large project that I've been working on since December and actually started in Vegas 20 so already through a major title update and multiple builds in VP21. Cannot express how horrible of an experience this was but again, this is something that no one should be doing. I learned the golden rule of video editing and that is to NEVER update anything mid project.
With that said, I've now run through maybe a dozen or so videos with build 300 and do enjoy a lot of the improvements that have come with it. VP21 seems to be more stable for me, the decoding for preview playback is a huge improvement, and I swear my renders have gotten faster but don't actually have any hard numbers to support that.
About the only thing that I've noticed that is worse is VP21 building audio peaks. It seems to take much longer for that process to finish compared to build 208 and even back on VP20. For the general content that I am producing though it is not nearly as much of an issue, I hardly need to rely on the audio wave form for it, and with larger more complicated projects I don't expect that it will be an issue by the time I get around to actually needing the wave form.
I know a lot of people on here are running into issues with build 300, and I expect I'll eventually run into some of my own. But I wanted to call out the good when I can.