I think they're ugly as sin....but I love how mine shoots.
I've swapped barreled actions several times and they always maintain zero.
I use mine for NRA highpower so I adjust length of pull and butt plate height/rotation for each stage (standing/sitting/prone).
I also added a 3D printed riser on the bottom for more height in standing. It doesn't look great, but it really helps my standing and sitting positions.
I have a set of the Large grips installed. I really like them for my big hands. If I only shot slow fire I would probably want even larger grips. The large grip almost fills my hand but is easy to release and re-engage during rapid fire stages.
I don't shoot weak side so I can't comment on your question about the cheek piece.
As far as magazines I've tried several brands and I really like the ARC mags. They click into the chassis effortlessly, but with almost no slop/play. And they feed flawlessly with my Archimedes action using 6XC and 6CompMatch.
I have a JAE-700 and an Eliseo Tube Gun. The JAE-700 is very comfortable, but not as adjustable as I'd like it to be for HighPower comps, and the Eliseo is very adjustable, but I don't prefer the AR-15 style ergonomics.....The XYLO is a very good middle ground. After my business picks up I'm hoping to buy another XYLO and Archimedes action....I'd like to build a .223.
Several folks have noted that the titanium rods that hold the butt plate assembly have loosened on them, mine did as well, but after I tightened the set screw holding them in, I haven't had any issues since...that was about 1000rds ago. I didn't over tighten it either, just snug.
Good luck,
Ross