My understanding is side stitching plays a role in mattress durability: the stitches go deep into the mattress through the springs and other layers and back out to hold everything together to the sides. My only slight hesitation with Hypnos is from pictures and videos it looks like some models leave quite a bit of space between side stitches, sometimes making the sides look uneven or loose-fitting. The royal warrant thing is pretty cool and there's much less price premium than Vispring or especially Hastens.
I haven't been able to try Hypnos since there are no dealers near me. No direct experience unfortunately but here's a bunch of random thoughts lol.
