I've had no experience of this (nor know of anyone else who has).
Personally, I'm always a bit sceptical about these 'miracles' and their claims, especially when they start to make vague statements such as 'will activate the functioning of any sluggish part'.
My personal advice with these things is:
1. If it's not broken don't try to fix it - e.g. 'Prevents feather plucking'. Aloe Vera may be an answer to feather plucking in a bird that plucks due to irritated skin, as it can calm and cool the skin. It has no reason to help a bird plucking due to boredom, and in a bird that isn't plucking, it could theoretically cause plucking due to the bird over preening in an attempt to remove this 'stuff' from its feathers.
2. If there's a problem and there's a well tried and tested solution out there, then use that solution.
3. If you have a sick bird and have taken avian veterinary advice, but despite best continued efforts your bird is not recovering, then you have nothing to lose by suggesting alternative interventions. Conventional medicine is not the be all and end all.
It IS an interesting plant though and I might just keep a look out for one and try the leaf gel suggestion on myself the next time I cut or bump myself.