Is it possible to install this conversion kit on a tub with arm rests or does it have to be smooth sides? The tub brand is Maxx Avenue.

It may be possible if you are within the maximum tub wall measurements for the top and bottom rail, but it depends on the specific tub. For further assistance, feel feel to email a photo of the tub with measurements to info@cleancutbath.com. A product specialist will take a closer look and provide recommendation. Thanks!