Their website is unclear on this, but I'd venture the 'free' level of service for Iris is not aimed toward multiple locations all within one account. But I didn't see any 'terms of service' info on their website (took some digging to find it:
https://www.irissmarthome.com/myhome/terms)
It doesn't appear to explicitly state it, but it does refer to 'your home' as the location for the service to be used. That and I'd venture their website probably doesn't allow adding multiple hubs to one location, or multiple locations. So then you'd get into having to set up multiple accounts, but given it's not for 'your home' you'd potentially be in violation of their terms of service. Hard to say, but I'm guessing if you call them you'll find out their 'free' service wouldn't apply. There are also alert & notification limits involved, but no clear explanation of what happens when you exceed them (being bumped up to the $10/mo. plan most likely). There appear to be a couple of 'gotcha' areas where you'd have to be using the pay-for tier to access. Especially if you wanted to consider having tenants being able to use some of the more sophisticated options like door locks or cameras. Never underestimate the drain tenants can put on your time & resources for crap like this...
To me it seems like all of the babysitting this would require would very likely exceed whatever rate you'd be charged by a professional monitoring company.