The core of Windows 10 is stable and well functioning. The build upgrades might contain some minor bugs but as they are built on a working core, I can personally see no reasons not to upgrade as soon as a new build is available. In any case, I always read the the MS articles about known issues before deciding if I want to upgrade or not.
I've been using the insider build(fast ring) for some time with no issues. The only way I found to really give the new build a complete test is by
using it every day. If I were to either dual boot or run it in a VM there's a good chance I wouldn't use it that often to really test it out properly.
Just my 2c on the topic..
All my machines (real and virtual) are fast ring except for two. One is my wife's laptop (she likes the windows 7 MS Spider Solitaire over any other version and I can't make it work on any RS1 release). At the moment therefore she is back on 1511. The other is a VM I use to connect to one client who likes me to connect using WebEx. That also didn't work after 1511 and so I've left it there on 1511 also.
I would never have noticed it if all I did was upgrade a VM and play with it for half an hour. I prefer to upgrade, try it and if I can't get it to work as @CountMike says restore back and try later.
It is worth keeping on trying - TOR didn't work on build 14251 but now does for example. Apparently WebEx now works but I've not tested it (I can't ask a client to wait while I try a different VM - it makes me look incompetent).
Running well with no issues of note. Oracle even pushed out a test build of VB that works so it's back to normal here.
I clean installed 14271. It took less than 20 minutes.