There will be one transformer per fitting.
Each transformer will be around 6 inches away from it's respective fitting.
This is to keep the low-voltage / high-current 12v wires as short as possible, yet far enough away from the heat of the 50w halogen.
Yes, the transformers are designed to be shoved up the 'ole in the ceiling, and the light fitting then snapped in place after it.
These fittings are held up by a pair of spring-loaded 'wings', which are tensioned up by a part of the spring which gets compressed by the diameter of the hole, as you push the fitting into the 'ole.
To remove them, simply pull them downwards out of the ceiling.
You'd be fairly unlucky to come across an installation where the transformers had been screwed down in the void space and un-removable by simply pulling it out the 'ole.
Worst case, an access hatch of around 6" square is enough to work through.
But with any luck, you might not need to replace any transformers at all. It's a suck-it-and-see thing.
Regarding price of LED replacements, that was just an example.
It's the ones I used.
You pays your money and make your choice.
Perhaps buy one and test it in the various locations before splurging more cash.
I'll just add that cheap LEDs tend to have poorer colour rendition, worse / unknown flicker, and poor lifespan.
It's not the wrong one, and you won't damage it unless you do something silly.
