My Chord Sequencer was never removed from the OS of an arranger that had it...

It was merely removed from subsequent models (that had quite different OS's). A hardware arranger does what it does from the day you buy it. Bugs are fixed, to a certain extent, but one of the drawbacks, that I consider that 'open' arrangers suffer from is a certain degree of acceptance by customers of issues that may or may not (or may at some indeterminate time in the future) get fixed, but definitely impact it's usefulness at the time of purchase.

Add to that the issue that, as newer CPU OS's and hardware gradually get added, there is the problem of new problems getting ADDED as new kernels, drivers, OS's and the like get updated. Even in the studio this is an inconvenience (or more, depending on the level of client you work for), but live it is a catastrophe waiting to happen.

While Dom's customer service is second to none, his very lack of size also has it's dark side... that revenues are not sufficient to do the style and soundset development that other arranger companies can afford. One step forward, one step back.

Me, I think I prefer the more 'closed' approach... give me an arranger ALREADY voiced and styled well, with NO dealbreaker bugs at all, and if it gets around to fixing some of the smaller niggles, cool... but if it doesn't, I've still got something bombproof for live use. If an 'open' arranger provides this, so much the better But trading flexibility for reliability for the live musician seems a poor choice.