so are zoo-med heat pads good to use? no hot spots?

because thats what im using right now. the pad is right up against the tub and i have a probe directl on the plastic bottom of the tub and it reads 90. and i have aspen bedding but they always move all the bedding and lay right on the plastic. so i was just making sure that the zoo med pads are okay. (they are both controled by one dimmer.)