For some reason I can't respond to the thread I created so have had to create a new one to follow up.

Historically in 'K2 Parameters - Advanced - sh404SEF integration' there are settings such as 'sh404SEF URL prefix for users', 'sh404SEF URL category prefix for items' and 'Use 'Title Alias' (instead of 'Title') for K2 URLs '. We use all three in conjunction with sh404SEF and we get our nice SEF urls.

The point which has not been clearly answered is this. In K2 v 2.7.0. these parameters have been decoupled, so will the historically nice SEF urls now lose their 'prefix for users' or 'Title alias' etc?

Weeblr have told me that they expect upcomng K2 plugins for sh404SEF by JoomlaWorks to resolve any changes. Upcoming commercial plugins are also announced by Fotis.

Logically, there is no problem, but I am also reluctant to upgrade to K2 V 2.7.0 at the moment, although I really really want to!

I would recommend to wait for a few days for the sh404sef plugin to be released.
In the meantime you can update a dev site (if you have one) to be 200% that nothing goes wrong with 3rd party extensions.

This will ensure that your site will not suffer, even if it is for a few days.

One plain and simple question. Is everything which was possible in built in integration in 2.6.9 supported in this plugin. Can't make all parameters from the screenshots.

Yes :)

So I missed in the release notes the fact that SH404SEF support was going away until a new plugin came out to provide the same friendly URL functions I had with SH404SEf and K2 2.6. So I upgraded to 2.7 and blew away my friendly URLs. Then I attempted to recreate the URL structure, which was impossible because of the neat functions that SH404SEF provides such as to include the last two categories. The only solution then was to roll back the site, or don't add any new items in K2 or to at least code them manually in SH404SEF. This was frustrating to say the least. The end result was that after a week of waiting for the new extension I decided to move away from K2. I'm trying to be nice as as write this, and I wonder what others did with production sites that weren't carefully staged. Kudos to Joomlart and their K2 import tool which saved the day, but in the end the whole thing has been very frustrating. What's worse is that I had ten zillion leftover URL's that had to be taken out of SH404SEF through SQL queries. I'm sorry this happened and will much more careful next time, I have good backups but don't stage that particular web site. I just needed to post my frustration.

I am sorry you feel this way Jim.
On hindsight I think you could have tried downgrading before going into this hassle.