I don't see a problem there, except for the process related issues in doing it two different places.
I've had some small issues with the new one that I can remember:
1. Some (very very few) schedules were created incorrectly. This bug has been fixed in current version
2. No devices were added to the schedule despite USM displayed so. This has happened just a couple of times that I've heard of but since I haven't found any steps to reproduce it, support hasn't been any help. Still waiting to see if it happens again..
3. I don't think multiple maintenance_mode instances is supported, which means if primary hub goes down you're left without it. You can configure secondary nasses to use the maintenance_mode on the primary hub, though.
All in all, it has worked pretty well and for me the great thing about it is, that it saves maintenance windows into the database. Check this out: Moving maintenance windows to SLO exclusion periods
-jon