Thanks for updating the 12.3x48 documentation and the links. I have a couple of thoughts.
It really seems like if chassis cluster is NOT supported, as it would imply by your comments, in the early releases, this should be explicitly called out in those pages as well. As a general rule my thinking is a feature exists unless told it does not. So if I read that 12.1.x47 description I might have a reasonable view that I can use dynamic VPN on branch chassis cluster. So I feel it is just as important for those previous pages to say
Chassis clusters are not supported
As it is for the x48 to say
Chassis clusters are supported
I do like this format where I can switch releases easily to see what changes in software releases. What would also be nice to have is the ability to do a similar type of switch for the hardware platform at the right. So that if I don't see what I want on this page I can switch platforms to see if I get what I'm looking for.
Also if there were some way to generate an "change log" of sorts that shows what is different among the releases at a glance this would be helpful in these situations too.
Feature explorer is better for this type of invesitgation as it does list all platforms then that have the feature along with the software release where it was introduced. But what is less helpful in the feature explorer interface is the arrangement of multi term searches. Drill into SRX650 with 12.3x48 and then search for "Dynamic VPN". the results are large because it does an or and arranged alphabetically instead of prioritizing results that have both terms.