Of the two №1 seems more up-to-date. Both contain broken links; №2 contains broken images. I'm not sure why both of these pages exist; maybe the second one made sense when transactions were a development preview, but now that they are a mainstream feature within Couchbase Server, I don't know why we need №2. Do you think it's worth getting rid of it (with redirects of course) as part of this issue?
Simon Dew №2 was a PM request as an SDK-neutral landing page to be linked from blogs about transactions - and not subject to the changes that Server docs can undergo.
Note, the other extension libs to the SDKs also have pages there - RTO and encryption.
A more in-depth history is available if you ever have the time.
In future, we may be able to re-use content from the very similar Server page, and this is probably what will happen.