Many coaches are a great asset when it comes to equipment. They can let you know when it's time to change boots, or when your blades have no rocker left, or need to be sharpened, etc. They may even have an opinion on what you might want to look into (such as what level of blade or stiffness of boot, etc.) Others have no idea about equipment whatsoever and won't even offer advice.
With all of that said, most coaches aren't trained in actually fitting boots. They don't know what brand will fit what foot the best, nor do they know the shape/oddities/tracing of your own foot to the point they would be able to recommend one brand over the other.
Regarding the heel height, yes, there is a difference between Jackson and Reidell. There is also a difference between Harlick and Edea (according to one of my friends who had both). While it might throw off some things at first, it's something that you can get used to in time. New boots are going to throw things off a bit, anyway. Who knows, my friend could all of a sudden do moves she had been struggling with once she got the new boots, but had to work to get her backspin (one of her best elements) back until she got used to them.
Regarding the blades, again, while coaches definitely have some knowledge of blades and what is okay for each level, there may be a reason a trained fitter might like one blade over another, especially with a certain boot or certain skater. I'm actually not sure that Comets really are a direct progression from Aces - honestly, I've seen more people go from Aces to Visions than Aces to Comets. And many of the people I know that had Comets hated them due to the flatter, 8 foot rocker and different spin profile. Like someone else said, they were okay for most things, but spins were an issue. Generally those that didn't like them either went back to Aces or up to Visions. Just something to think about as these tend to be personal preferences and decisions.