Oh across the breeding world there are many fancies, pending species and breeds, and it become trends..just because many do it, doesnt mean its the rigth thing for the animals health. It doesnt mean all mutations are bad, but you need a bit of knowledge and tread carefull to find if a new mutation serves the breed or not, and even then to follow good breeding principles rather then rushing to produce it up for a market.
I dont know the background of the hago' mutation so wouldnt know if any bad health is conected to it beyond what can be deducted in general..
1 its not natural for budgies to have feathers that way, if it was functional for birds to be like that you would find it in the wild too, and I can but imagine it would have its backsides for the animal in many a way.
2 the fact that often to get stuff like this they botleneck the lines..so you have various degrees of inbreeding, which always is a bad thing, and inbreeding depression leads to many health issues over time.
Ie anything that variate from the norm of the breed or spicies I would be sceptical about, untill I had time to research it and get proof that its not harmfull to the animal, or bring about it larger risks for bad health.