As noted, the Mystic Stealth is a very different fit to anything else I have ever used.
It is a nicely put together harness, with good construction & very innovative in the use of the neoprene padding that doesn't take on water.
Sadly for me, I have used mine twice in powered conditions - 25-30 knots and on both times, I had to come in to take the harness off, as unfortunately, the internal waistband is thicker/more rigid than my RRD Y25 Carbon Shield and it feels like my rib cartilage/10th VB rib is about to snap (again).
The RRD carbon Shield is stated to have a low profile spreader & putting the two harnesses side by side there is little if any visible difference, but the difference riding is night & day - the RRD suits my back & seems to spread load better, as I have taken the Stealth off and gone straight out with the Shield.
Definitely try before you buy, but bless them, my retailer (CBK Hayling) offered a full refund