I have an HQ Avante with ProStitcher and love it. I do not find the software difficult to use and the few times I have had to call a Tech at HQ they were amazing, patient and a lot of help. There are also many groups online dedicated to the ProStitcher. As far as portability between machines - I do not know about that, but I do know that in the discussion groups it is clear that those members who have other machine heads (non HQ) with a ProStitcher appear to have different software capabilities at times.
There is a "ProStitcher Posse" on Facebook and also a Yahoo group (now moved to Google groups.io) - both groups are extremely active and moderated my HQ Educators willing to help. You might want to join that type of group to get even more information. Also - you might try to call HQ hotline and ask to speak to a Tech. They, i am sure, would be happy to answer the portability question.
Good luck with your decision - Big investment so it is wise to ask all these questions before.