I am pretty excited for windows mobile 10 and want to try it ever since. But the list of known issue always hold me up as there was some critical loss of functionality which I needed as I have only one windows phone (lumia 730) and I can't take risk as my daily driver. Build 549 doesn't have any major known issue and thus finally decided to take the plunge.
Install the windows insider app and start the upgrading process from 8.1. BTW I didn't reset 8.1 and upgraded with my all my apps and data.
Upgrade process went smooth and my phone was on windows mobile 10 TP. There was a perceivable lag and lots of loading and resuming and random app crashing, therefore decided to do hard reset, opt for to sign in later only to found you cannot restore your backup (my list of app installed was needed). So hard reset once again now to sign in right from the beginning and restore from backup. It was cumbersome to say the least. Here are my impression and observation of build 549 :-
1. Been stable and not even a single random crash.
2. There still perceivable lag as compared to windows phone 8.1 in unlocking (there is splash screen of choosen accent colour before showing the lock screen), start screen swiping, apps loading, and in overall responsive of the phone. But it's not that bad and I am already getting used to it.
3. SMS and Outlook tiles are not updating to show unread mails (same for desktop) and sms.
4. Apps crash when trying to access file system through file explorer.
5. Battery life is comparable to windows phone 8.1 and I got through the 24 hours without charge (I am lucky ??)
6. No heating issue.
7. Apps in background list have multiple entries of the same app.
8. Edge is slow and no option to change my homepage (or did I miss something ?).
9. Lumia camera show there is a better option. I obliged and uninstalled the lumia camera.

10. Random brightness issue (sudden increase of brightness to its fullest and I mean really bright). Workaround by resetting brightness from settings>extras>display. BTW why two display settings, should have merge them both.
11. Store function fine with very few niggle. Also on this note if they are release a whole build, why not do with latest apps on board. I mean there were 50 plus app updates on startup.
12. Not turned on cortana even once.
13. Notices how app data is now not counted in app section but showing in "Other". Also moving apps from phone to SD card and vice versa is slow. Also was able to move some critical settings app (display,sound etc.) from phone to SD card but then revert them back to fear of unnecessary new issues.
14. TXT files saved on my onedrive are not opening on onenote.
Overall I am happy with the build as my daily driver and will continue with windows mobile 10.