Not all of us possess the mechanical abilities do our own brake upgrades. Everything comes at a price. The person who engineered my car recommended IDB because of there good work.
When i got my brakes, it was a simple bolt on. I didn't have to pissfart around looking for parts. Also don't forget that ae86 parts are rare so extra work has to be done to make other parts fit. The rotors are 11 inch vented and slotted with huge 4 pot calipers. I have a 1g-gte in my ae86 so anything smaller would have fried under stress.
Obviously, if you can do it yourself and you have the time go for it!