The latest build of W10M preview is not ready yet. Yes, the performance is ok but it's not enough. It's still feel unfinished and very inconsistent, Groove music is still very buggy (quick access lags; when you select a song sometimes it won't move to the next; if you pause for a long time and then press play, Groove will start playing the previous music selection instead of playing the actual selection; sometimes it's just unresponsive and needs a reboot), photos apps still crash at times, emails are not working properly (most of the time my hotmail emails are not even synched), the start screen sometimes goes blank, MSN weather live tiles still displays blurred icons, some app icons in the app list are blank, the app store tile never displays updates notifications even if notifications are turned on (and not just the store BTW), battery is still draining like crazy, camera apps have huge slowdowns at times and get unresponsive, when using Rich capture it sometimes takes ages to render, hamburger menus are still completely inconsistent across the board, UI is still very confusing (contextual menu with 3 dots gives different info than long press or hamburger menu or some info are burried deep down...) and so on...
The goal of MS is to imitate what Apple did: a few devices to have a consistent experience on every device and keep control over these. Right now, the insider program behaves completely differently even on a low amount of lumia phones and it supposed to be released "soon". It's even inconsistent between phones of the same category. Some 930 are working okay, mine is quite buggy but usable while it's a disaster for others. If the phones were the exact same, the experience, by now, should be unified and the number of issues should be narrowed down and consistent for easy fixes. Which it clearly isn't. Everyone is reporting different issues everywhere so, there's either an issue with the hardware or the software. But if a company as huge as MS can't handle a limited amount of devices, it is concerning.
Besides, even if some issues are maybe not a deal breaker, at least for some, having a web browser that's constantly slow or buggy or a music player that's not on par with the competition or inconsistent UI (which is how we actually interact with the phone) is a deal breaker, at least for me. And we shouldn't accept the fact that it's "usable even if buggy" because it's MS. When a company releases and unfinished game/product/service, everyone complains. If MS releases an incomplete OS, we should be against it. Being a ****** does not mean you should be treated like crap and get subpar services or accept things for whatever reasons. And shipping a new hardware running an unfinished OS is a joke. MS is not firefox or Oneplus...