Browneye, you need to keep reading. There's a LOT to this. Bolton's kit is taking care of a lot of the shortcomings many RAD owners complain about. He is not associated with RAD in any way. I would guess RAD would like to see him go away.... He started in this offering much the same for Pedegro owners, and became pretty popular there.
As far as "upgraded", stuff that come to mind here-
The KT controller is able to control and feed the motor significantly more amperage than the OEM controller. There's nothing held in reserve. You get what the battery has to offer.
There is no locked in "soft start" that dulls the stock Rad motor performance. When you tell a KT equipped bike to go, it does just that, right now. No delay waiting for power build up. This leads to a much more spirited bike. There's none of that accelerating uncontrollably at low speeds either. Your cadence will determine your speed. Not like an on or off set up you hear about on some bikes. You want to go 5mph in PAS 1? Go for it. You want to go 12mph in PAS 1, start pedaling!
As far as that goes, nothing is locked down. You're the boss.....
Many settings (parameters) are able to be set by the owner. An example might be where you want to control the max amperage you want the motor to see.
Another example might be how much voltage you want available in PAS
What level do you want the PAS to be in when the bike is powered up?
Do you want the throttle hot when the bike is powered up, or do you want to wait until the bike is moving?
This is all in addition to what size wheels you are running, the max speed you want the bike to run, American calibration or metric, and the rest of the "usual" stuff.
There's cruise control available at anything over about 7 mph, and regen w/levels that you can set. There's more I'm sure. That's just what comes to mind.
As far as going out and sourcing your own KT display and controller, then matching it's wiring to the Rad on your own, that's what I did, and I'm no rocket scientist. I did go with a "kit" that came with the controller and the display, along with the brake handles. This minimized the wiring difficulty as all that stuff came matched. All I had to do was match the battery (easy) and the motor (not too bad).
I would caution though, that not all KT 35a controllers are the same. You need to be pretty careful to get what you think you are getting. Don't assume for instance, that the controller will have regen, cruise, or be set up for lighting for instance. You have to confirm the controller you're looking at has every feature you're looking for. This is not for the faint of heart.....
And no, the RAD display is not compatible with a KT controller. I found that out the hard way early on. Didn't realize it was totally different. -Al