I use this extensively in my jam sessions. Basically I activate hold, and press a chord to arpeggiate. When I need a new chord, I just reach up and strike it and the arpeggiator switches all notes to new chord. After the latest updates, (I think it happened after the 1.1.2.5 update) when I strike a new chord, the notes are added to the arpeggiation and not replacing them as before. I received a reply from Carson within a couple of hours (amazing job, thank you support team) that it is indeed a bug and they added it to their list to address in the next update. Until then, I will find a workaround with software arpeggiation. This is still my favorite mono synth and I commend Dave Smith and all who worked on giving us such an amazing piece of hardware.
I was unaware of the existence of Arp Relatch. So I read the manual entry about it a bunch of times, and I still don't understand what it's supposed to do. But there's no obvious difference under the new OS whether it's on or off.