alpha or beta, it's just a label assigned by its authors. The beta version of 7-zip is actually very stable. It would have been labeled "stable release" by most other authors. So a alpha or beta is just some preference of the author of 7-zip. I have been using beta 9.38 ever since it's released and never has any problem. Check out their forum, people also say the same.
Yep, been using 15.05 beta and so far the only thing that it lacks is RAR5 support, which unfortunately does not support -_- apparently for the dev, it's not a big deal :/
Igor is working on RAR5 support. a few days ago he said this work is more than 50% completed. So hopefully we'll see RAR5 support in next beta.
It's been in BETA/ALPHA for more than a year. I stopped using it due to this slow development. WinRAR FTW
beta... alpha... just words, sure the development was stagnated for some time, but it's back on track. Hope you're happy with WinRAR in your little happy world lol