Anyway in my googling I found out that my Lumia 535 had a Windows 10 upgrade but the funny thing is you had to download another app (very similar to the desktop version of the OS) to get the upgrade. My question is why not just push the upgrade via the regular phone update built in to Windows phone 8.1 like what Android or iOS?
I did a hard reset (and wiped my SD card too) before updating using the Windows 10 Upgrade Advisor App (available on the Microsoft App Store, search for it on your phone) it took about an hour plus to update and get to the start screen (not including download time). YMMV.
After updating I immediately checked Phone update and low and behold there's another one... Now why upgrade people to an old build? Oh Microsoft...
So I updated to the latest build. I've only had one (1) unexpected reboot. And this was early on when I was poking around with the settings. So far build 10.0.10586.164 (same as my laptop by the way) has been quite stable.
Of course my 535 is a bit long in the tooth so a bit of sluggishness is to be expected. Keeping that in mind, I do enjoy the little touches like being able to reply to the text or fb right at the notification or action center (yes it's late to the game but still appreciated).
Speaking of the Action Center & Notification Center. I really like it. It's one of those changes that makes the device easier to use. The settings screen will look familiar to Windows 10 desktop users as well. The Start screen with live tiles and the lock screen is basically the same.
Most of the built in apps get a refresh. I especially like the email, calendar, and Office apps refresh.
You also get the new Microsoft Edge browser.
The app situation on Windows 10 Mobile is more of the same... YMMV. It really depends on what apps you are using. In my case I am happy with the selection (although this is my secondary phone)
I've customized Cortana on the phone and the settings have synced to my laptop. Sweet.
Press & hold the back button to go into Task Manger
Press & hold the start button to enter one-handed mode (a reachability clone)
So far, I'm really liking Windows 10 Mobile on my Microsoft Lumia 535. The sluggishness makes me wish I had a higher end device to really enjoy the experience but all in all this is an update I would recommend to Windows Phone fans.