I have been using the R Studio 1.4 daily builds (OpenSUSE 15) for several months now, updating my installation2 or 3 times per month. No major issues all the times. I am at 1.4.1081 now (last preview), 6 commits behind the current preview. Works well. From past experience I assume the 1.4 release will happen soon.
I went for 1.4 because the support for Python is a lot better than with 1.3.
And Markdown Visual mode is nice, although that came with some small glitches in the beginning. Normally fixes are available faster than I can report issues.
So all in all - If you can cope in the moment with a tiny tiny bit less than 100 percent finished R Studio go with the preview. In a short time you would probaby change to the 1.4 release anyhow. - If you need highest available maturity, use the 1.3 release.