It says it works from anywhere, but then only gives a number that works from within the US. How are you supposed to use this service while in another country and not having access to a US sim card?
Sounds like that's a problem that Magic+ can solve for 100/hr.
The regular version of their service still appears to be US-only[0] (last FAQ item). I suspect that Magic+ is also US-only and they've neglected to mention it specifically on this page.
If you are in the target group that is willing to pay $100/hour for a virtual assistant at the beck and call of an SMS, then the $0.20 or so for the SMS roaming charges seems like small change...
Assuming they have a +1 ... internationally available SMS number. 5 digit shortcodes aren't guaranteed to work globally.
I don't think US shortcodes are reachable internationally.