Laterite is not a fertilizer. It is a clay. It will not burn the roots of your plants. Laterite came into use at a time when aquarium substrates were lacking in iron, and people did little, if any fertilizing, so their plants tended to be short on iron. Today we have several choices for getting iron to the plants, mostly by using a chelated iron. Chelated iron is bioavailable, where iron oxides are only slightly available to the plants. You can use laterite if you wish, and know it isn't going to do any harm, but if you follow a "modern" fertilizer dosing scheme you don't need laterite.