I'm thinking of switching from mijosef to this extensions. But a few things are very important for me. My docman links have to stay the same (without id). Currently I'm having problems with multilanguage (mijosef creates urls with lang=nl and lang=nl-nl and lang =en and lang=en-gb. It is very important for my that this stops happening. Is there a way to test of your extension is working the right way?
I am afraid we cannot guarantee all those conditions, especially keeping exactly the same links for Docman. That is very unlikely to happen as we simply use the Docman router.php file (for Joomla SEF), but again I can't be sure.
We do not provide a test version, that's really hard to do for GPL-licensed software, but we do refund in case something goes wrong, so I would encourage you to do all your testing anyway.
To be honest, I don't have much feedback about Seblod. There is no reason it does not "work" with Seblod, as it's a standard Joomla extension, and it provides a router.php file for Joomla SEF.
For Seblod, just like for Docman, we do have a MijoSEF importer, that will import existing SEF URLs from MijoSEF. So mostly all your existing URLs can be imported as "custom" URLs. URLs created in the future may or may not follow the exact same structure, but existing ones should be ok. Again, that requires validation by testing on the real data.