Well, “officially” you shouldn’t run production solutions using Beta software.
HOWEVER, we (Servoy) have been running webclient on our site for quite a long time, and there are several other customers doing the same.
Since we’re a couple of months away from the “official” release - you can start building solutions in 3.0. Because, in our experience, by the time you get it built (ususally a couple of months) - 3.0 final will be released.
If you need to deploy in the next 4 weeks, then you could use 2.2.5 and upgrade to 3.0 when released.
It’s really a matter between you and your client.
Hope this helps.