Save your money until you can afford good disk brake calipers...be they mechanical or hydraulic...also make sure to maintain the brake pads and have an extra set. Ebikes go through brake pads far faster than a bicycle...they are much heavier and require more braking to slow and stop thus wearing out the pads faster...better off with metallic pads though without maintenance they will get screechy but at least everyone hears you as you are braking.
I have a pair of TRP Spyre carbon mechanical disk calipers and for mech cals they work quite well but they are not inexpensive.