FYI for those in the same grandfathered Eagle Standard situation since I'm fighting through this right now:
The benefit is F360 commercial gets added on for free, which is a total steal.
The disadvantage is, well, if I need Eagle Premium for a project, how? I used to have Eagle Standard monthly, so I could switch to Eagle Premium on a whim when projects called for that.
The answer is, you can have an arbitrary number of licenses tied to your account at any given time, and you just have to do some hoop jumping to assign them.
So for instance, I need Eagle Premium right now, temporarily. While not touching my $15/mo "F360 with Eagle Standard" subscription, I can simply ADD a $60/mo F360 subscription for 1mo. which comes with Eagle Premium.
I was told this would "automatically" apply the Premium entitlement, but Eagle's pretty bad about fetching new licenses - I'm not sure if it simply won't "automatically" do that, or if it'll just take a stupid amount of time before it takes.
In the mean time, I went into my control panel on Autodesk and went to User Management. I unassigned both entitlements from my user account, and about 15min later verified that Eagle would pull a "Free" license on logout/login. I then assigned only the license seat including Eagle Premium. Another ~15m or maybe 30m later, I now have Eagle Premium for the next month.