You can go to your local lawn & garden dealer to play with a few display models. Not run them, but at least check the balance, weight, general UI, how easy it is to get the line spool off (can vary greatly from your son being able to do it with his hands vs your needing a screwdriver to pry and getting muck all over your own hands doing it, lol).
I prefer straight shaft but it matters less than one with a commercial engine. Less vibration, easier starts, less picky about fuel quality or age, more power, easier to find parts, etc... even if some of the parts are obscenely priced like $30 for a 18" piece of throttle cable with a pot metal custom shaped pin on one end. I rolled my own but it probably won't last as long as the original.