Yes very effective engine braking. (Un?)fortunately the 520 does not even have a differential so the rear is always "locked", like most ATV's. This gives it great traction but makes it harder to steer and can skid up the terrain that it does sharp turns on. The front is an open differential.
My preference would be for Honda market two versions of the 520: one like what we have now only with a conventional differential for the rear that can be locked. The other, say a P520 Extreme, as above plus with a locking front diff and a step up in tire size.
My other SxS has a locking rear diff and in all honesty it's left unlocked 80% of the time, when more traction is needed I first engage 4wd which is usually enough. Even though it's larger and heavier than my P520, it is easier on the yard, gravel driveway, and trails.
I think a lot of potential buyers that are attracted the 520's small size and dump bed as a little transporter to run errands, go to the mailbox, working in the yard, etc., end up going with other choices such as the small Mule, golf carts, etc. for easier steering and to not skid up the turf so much.