Well someone has to have the fastest ship and it probably would be the smuggler (A Wings excluded I assume). As to Rose' mechanical skills, I've no idea other than 'she works behind pipes'. But here's the text:
The system was developed by the technician Rose Tico using a computer system to baffle their energy signals.
This is basically the 'hacking is magic' trope- which we also saw with DJ when approaching the Supremacy. I'll believe you can access things maybe you shouldn't from a terminal (such as the Supremacy's shield controls), but I draw the line altering energy emissions from a spacecraft. No amount of computer work is going to change an F-16 into an F-22. More over, one might wonder why, if she can cloak these transports, the same is not applied to other Resistance craft. Fighters are much smaller than the transports and I'm sure they'd love for ships not to pick up on them instantly.
Because the entire purpose of sensors is to detect things. They ran a 'de-cloaking scan' which is pretty much what every scan is- the revealing of otherwise imperceptible things. Basically if the Rebels had loaded a transport with bombs and painted it black, they could have flown right up inside the Supremacy (or any other FO ship) because despite having the capability to scan for them, they simply don't. That's insane, yet we saw Rose, Finn and DJ do just that (albeit with a different objective).
Like the hyperspace tracking and ramming, it's one of those things that's going to be more of a headache going forward. A cloak on something like say the bombers or the fighters would be amazing- even if they have to, for some time, limit their output to that of the transport.