Aero is trademark name of the spool design of the Shimano spinning reel, so most Shimano spinning reels are Aero, like many Shimano baitcasters are Bantam. The Shimano Stradic MgFA is in practical terms the same reel as a Stradic with magnesium frame & machined handle, performance is the same in both reels.
Sealed GEARS.......I don 't think so, sealed drag ( waterproof ) and sealed bearings most likely, but Stradics do not have sealed bearings because they come with ARBs and those aren 't sealed, Stradics also do not have waterproof drag; the Tierra does have waterproof drag and CRBBs ( same as ARBs ).
Now let 's see, the Tierra is new, it took the place of the Capricorn so it must be a good reel ( the Capricorn was a good reel ), it has waterproof drag; the catch here is, the Stradic has been around for over a decade and it 's still is one of the best spinning reels around, it 's the old Curado of spinning reels.
Just for that reason alone I would go for a Stradic, I know I 'm going to get a dependable bullet proof reel for the next decade or more.