Keep in mind that "low" vs "high" is just how your switch works.
You still need to determine what braking mode you want to use, how much braking you want out of it, and get a motor and controller and battery that all support whatever that ends up being.
If you already have a motor, battery, and controller that you must use, you are stuck with whatever those limit you to.
So if you want control over the amount of braking while you ride, you must use a controller that has variable regen. I highly recommend using one that has an actual analog input for the brake, not just a switch input that forces you to then use the throttle for braking; it's much more intuitive and easy to use if it is it's own complete separate control. Then you can use a cable-operated throttle unit that is pulled by your spare brake control.
If you don't care about control over the braking amount, you can just use a switch on the brake control, but you're stuck with whatever amount of braking current that controller supports.
In either case, your battery must be able to handle the regen current (charge current). For instance, if your regen is say, 40A but your battery can only be charged at 5A, you'll destroy the battery by using it this way. So you must have a battery that is safe to charge at the regen current rate.
The battery should also be able to protect itself against damage that can be caused this way: If the BMS is a common port type, then it can protect itself against overcharge, but when it does this it will disconnect the battery from the controller. When this happens, the voltage inside the controller will spike far beyond the usual, probably above what the parts in it are designed for, and it can fail catastrophically. It's not really an issue if you are never near full battery when you start long regen braking events, but if you are at or near full, and regenerate enough to cause any cell to trigger BMS HVC, it could happen.
If it's a separate port BMS, then you are charging via regen only thru the discharge port, and it has no way to protect itself from overcharge, etc., but it can't disconnect druing regen so can't damage the controller. So...depends on which part is more important to you for which choice you make. (batteries are generally more expensive than anything else on the vehicle, and when damaged can fail catastrophically (even catch fire).
The motor, controller, and wiring are going to get hot from the regen braking, and so this wll reduce your ability to use the motor for acceleration and cruising, as they'll already be hot so further use of them will heat them more. At some point with enough heat, if you have temperature monitoring and limiting, the system will reduce power to or even shut down the ability to use the motor. If you don't have monitoring/limiting, then the motor, wiring, and/or controller will be damaged from the heat.
