I like the PGJ's and i hated the PGM's because of the nozzle set up....horrible set up...the PGJ is much improved and works great when you need what it offers.
I don't know a friggin thing about the Orbit 550660...but I do know that the I20 is VERY versatile..and will certainly be a fine addition.
Find the I20 specs here: www.hunterindustries.com
Sprinkler Solutions, Inc.
Arizona and Colorado
www.sprinklersolutions.net