The harp space on my Janome Magnolia 7330 is very small. I was a very beginner quilter when my DH wanted me to get a new machine & knew nothing about harp space at the time & the salesperson never mentioned anything about harp space. I say do your homework before purchasing an new machine.
Never heard of the two spool machines but I've looked it up & here's a short video on a treadle machine that uses a spool for the bobbin. Oh, I wish they still made those.
https://www.quiltingroomwithmel.com/...ine-video.html