Richard, I have an AJ and it is, without doubt, the finest dread I have played in over 40 years-and trust me I've played and owned many!
Tonally, however, it's a very different guitar from the J45/50.
The biggest difference, as you point out, is the longer scale but being rosewood as well as having a different bracing pattern also gives it a distinctively different tone.
The J45 is smoother and warmer; more restrained to my ears while the AJ is loud and quite forceful in its delivery.
The extra 1/2" of scale isn't really noticeable to me as far as comfort goes and I'm comparing it to my J185 with its 24 3/4" scale. It's all in the set up.