I'm using .99.84 out of necessity but I haven't run into any problems with Construct crashing during editing or testing (outside of my own errors). I've sent .cap's and .exe's to friends and they haven't had any problems running them other than the occasional person needing to update DirectX.
I used to have multiple versions of Construct installed and all I did was change the folder name. I imagine you can still do the same thing.
I've mainly just been using the physics and platform behavior in different .cap's though, so maybe other people can tell you what kind of problems (if any) they have run into with the newest unstable release.