It will be simplest of course to get a direct replacement with as much extra info as possible from the manu Verteci.
But, if you know what voltage you are using now, and are happy with the bike speed, the main criteria is a brushed controller that works with that voltage, although connectors and throttle function need consideration also.
Addressing speed/voltage: speed is controlled by the voltage you pass to the controller. If changing controller (or battery), consider the low level battery cutoff on controller- you don't want one that is too high for your battery voltage or it won't allow you to use all of battery capacity, and may not run at all.
Example: I had small 150w scooter w/ brushed controller. It says it is for 24v, with a minimum (the cutoff) of ~19v (iirc). So I couldn't make use of any battery power that drops below 19v. When confirmed it could handle higher voltages (I simply just tried it
), I had the option of running more voltage for more speed. I ran 48v on it for fun, but of course the tiny controller wasn't anywhere near capable of pulling enough amps to make good on that higher speed, except down a hill. Double the voltage, double the motor max rpm. . .
Voltage = speed. Amps = power to get to that speed. You want them reasonably balanced for the system components you are using. I hope that helps!