As part of considering the suprone position/setup, I thought it might be good to discuss some of its potential drawbacks:
1) Drag. The sitting position (as compared to prone) presents a larger frontal area to the airflow and most likely a higher drag coefficient (i.e. not as streamlined). Could be lessened somewhat by getting XC/race style PG harness.
2) Downward visibility. Reduced since your legs are in front of you. Guessing you can just lean your head over to one side if you need to see below you better. Paraglider pilots would face the same issue and they seem to manage.
3) Added weight / setup time. Spreader bar and downtube handles adding weight. Attaching and removing downtube handles would add a little bit to setup/breakdown time.
4) Harder to try out. Being less common, you'd either have to invest the money in a setup of your own (probably not economically feasible unless you could find a good, cheap used PG harness (maybe resell later, if not your cup of tea) and then DIY the rest of the parts) or find someone within a reasonable distance willing to let you try their setup. Further potential difficulty with the latter if their body side and/or glider significantly different than yours (e.g. big pilot trying to fit in a small harness, downtube handles don't fit you glider correctly, risers too long or short, etc.).
5) Stigma. It's certainly not the mainstream way of flying. Some probably view it as being for old pilots or those with a bad neck and/or back. Like Doug said, to each his own. I'd like to try both ways before investing in a setup. Who knows, maybe I'll eventually buy both and then just decide which way to fly that day once I get on site and assess conditions and mood. Interesting listen here on the Threshold Model of Collective Behavior (which I happened to hear on the podcast while driving on one of my trips to go train):
https://www.thisamericanlife.org/radio- ... act=1#play