Just installed new Windows 10 Mobile Build 10572 and my initial impression is the animations are surprisingly smooth but the performance is indeed worse. It tends to lag and some apps just show the lovable "Loading..." screen than usual, especially on Lockscreen and as basic as Phone app (talking about trying to dial up emergency on urgent, that loading screen will be a hell). So far as first time W10M Insider user, the build is fine but I think it's still far from being RTM quality, at least on my testing. Performance, bugs and more polishing is still needed a lot....a lot. Also app performance needs to improve further, we need less time spending looking at app banners and yeah Loading screen has to be "eliminated" especially on basic phone apps such as Phone, Messaging, Photos, etc.
Also I just run into issues currently that W10M doesn't detect my MicroSD properly, but weirdly enough Files app detects it while the rest isn't. So There is no photos, music, videos, apps, anything on SD card is present since the OS thinks it doesn't detect any at all.