Not sure it doesn’t, beyond the risks you’ve already mentioned.
On the other hand, there just aren’t that many devices that run S1 only. Many can run either S1 or S2, just not both at the same time.
And, on the third hand, the fact that ‘new features’ will never be added to S1 might impact some users, unless they have no plans for anything than their current use.
Adding older equipment to a large S1 only setup makes sense, it gives you additional devices with minimal expense and without having to upgrade to S2 and possibly split the system.
I’d add a used S1 to my mom’s setup as it is S1 and she is happy with that. Since she only listens to one local talk radio station new features won’t impact her.
If it was my system I might still go used, but I’d not pick up anything that wasn’t able to upgrade to S2, hoping to minimize the pain when I finally had no choice but to upgrade.
