Works fine (no crashes) for me with 10.5.4 and 10.5.3, had a total of 1 crash with 10.5.2. I've got the paid version, but I cannot believe that license status has anything to do with the problem being seen by the OP.
I'd suggest the original poster send mail to
OmniDiskSweeper Support and get the issue resolved, either by examining the crash logs or issuing a refund. I don't think I put words in their mouth by saying they don't like to have unhappy customers and will try to make you happy. If you just sent in the crash reports via the Omni crash reporting tool, no human may actually have seen the report. When you use the "Send Feedback" command under the Help menu, someone does see it. When I did so last week with an OmniDiskSweeper issue, I got an answer from the head of Support & QA in about an hour.