1) When you change the "parameters", there is a bug in that they don't save properly - for example, i changed the table prefix and directory path. I ran the upgrade and it used the "old" settings. I closed out, ran it again and it used the "new" settings so there is a problem with the parameters settings.
2) Most importantly, what JUpgrade does not warn you about is that it puts all the "new tables" into the existing database. I wish it had warned me of that - now my legacy database is muddled with a bunch of new tables and I had to restore my site/db.
3) And of course the final piece - it simply did not work. None of the articles, sections, categories, etc came over. It pretty much failed all the way around yet gave no errors or other warnings.
This is an unreliable/buggy extension to say the least.
And the site I attempted to use this on was VERY vanilla. Not a single 3rd party extension - was literally just a plain 1.5 site with articles.
1) It may be "highly customizable", but that is only from the backend/style sheet perspective - don't get this module if you are looking for something that has an easily configurable interface. The interface is very limited.
2) The "cool" looking examples on their site are not free. They should also tell you that up-front. When you buy the core module, you get 3 basic templates that are pretty undesirable. To get the module to look like what they showcase on their website you have to purchase additional templates.
There are other modules that are capable of doing more and are cheaper or even free.
This is likely a great module for those wanting extensive control and willing to do backend style sheet/template creation, but it is not an easy plug and play module that will give you great results.