Tom, I can't find watermelon on any list of toxic or not. Is it ok to feed Sulcatas watermelon? I eat a lot of it in the summer. He can help me out by eating the rinds.They do two different things. Both are good and both have their uses.
I prefer to use the Mazuri like another food item. I feed it as a meal once or twice a week. This is handy for people in cold climates with frozen winters where there is no food to be found outside, or for people like us in hot climates when most of the weeds die off in summer and the new weeds don't start growing again until the winter rains return. I feed a lot of grass hay and cactus pads all summer long, along with grape leaves and mulberry leaves, but in fall when the cactus, mulberry and grape leaves all die off and stop growing, I've got nothing to feed my tortoises until the weeds come back after the rain starts. Mazuri helps get me through.
The ZooMed stuff is great to soak and mix in with grocery store greens to add fiber and variety. It usually takes a tortoise a little while to get used to eating the Zoomed stuff. Most tortoises the to the Mazuri pretty quickly, although you occasionally find one that doesn't seem to care for it much.