I'm thinking about installing the iOS 10 beta to my main phone but couldn't find any decent info on its stability for a daily driver. macOS is more dangerous anyway so I'd only get into iOS beta.
My general guideline for prerelease OSes is: don't install them on anything you need to actually work. If you have a spare device and want to mess around then go for it, but putting it on your primary phone is complete madness.
Have been using the iOS and MacOS betas since day one without a problem as my day to day devices. There are certainly bugs and crashes here and there but no deal breakers. However, I wouldn't recommend it for most anyone, since when things do break I can easily find work arounds, where the average person may not, and if compatibility for something you rely on breaks then you are out of luck if you don't have extra mac laptops or phones to work on. These betas are far more reliable than previous years. To note, you have a typo in your title. "macOS" is a thing, "MacOS" is not.
I've been using iOS 10 beta since Public Beta 1. Like others have said: mostly stable, with terrible battery life.
One thing particularly annoying for me is HTTP Proxy: it seems that as of Public Beta 2 setting it will cause the device flood the server with many requests. I'm using GlimmerBlocker and on the server side it'd get 1k+ threads almost instantly after I turned on the proxy setting on the iOS side.
Other annoying bug is WebKit View would lose width setting randomly in 3rd party apps (e.g., Reeder).
Don't do it. I had to revert back as it rendered the phone useless. It has so many bugs, that even simple things were not working properly (for instance if you have a group of applications and you want to open one, the first action that happens when you tap on the icon will change the mode to editing [when the icons are dancing and you can move/deleted them]).
I've been running Sierra, iOS 10, and watchOS 3 since the first beta. Battery life on iOS sucks if you use any apps that make heavy use of GPS, but it's not OMG UNUSABLE bad. Just annoying.
watchOS 3 is fantastic, like beta 1 was better than the release version of watchOS 2.
Don't install the beta. iOS 9 beta literally bricked iCloud backups on my iCloud account. I had to get Apple Engineering to wipe everything. Even deleting backups wouldn't fix it, it had to be cleaned up in the backend. Yuck.
The production iOS 9 cloud restore 'bricked' iCloud photo sync from my devices (iCloud Photo Library, not Photostream which was fine).
iCloud Photos wouldn't update on the devices because iOS 9 thought the devices were still restoring from backup. Apparently a known issue with tedious workarounds involving mounting phone as a drive.
iOS 10 beta fixed the issue (perhaps expectedly, as it wouldn't make sense to preserve a pending iOS 9 restore after update), and all the iCloud Photo Library syncs worked again.
The latest beta ironed out a lot of interface bugs I was having, and the battery life is a bit better. But don't expect iOS9 battery life, because comparably it's atrocious. Par for beta course.
Running both, iOS 10 beta has been pretty stable mostly, much better than previous iOS betas, and Mac
OS Sierra beta too. They're good enough for daily use but obviously not for any critical stuff.