Hi lampreialopes
You have a JA Pro (JA+GK) which allow to download everything in Gavick ( templates - extensions - themes ) and also joomlart templates , with complimentary extensions ( extensions installed per single template as seen on our demo site ) it doesn't allow to download extensions stored under JAEC Membership that needs to be purchased separately .
If you look at THIS PAGE it is stated Everything in JA Pro & and Ja Pro doesn't include JAEC where ja megafilter is
Hope it helps
Regards