Did a lot of research before getting mine. It is not set up yet, I ordered the wrong metric to US adapter fitting. Bigger is not necessarily better - just different. If you oversize too much, the filter media will not advance as quickly - potentially leaving what you filtered in the water longer to break down. I guess it depends on your goal - lower nitrates and nitrites, or maintain them.
My tank is on the smaller size, and at least for a while will not be heavily stocked. I went smaller simply to avoid the filter roll taking days to advance. Even then, the roller I purchased is rated for a tank several times the size I am going to have. I don't really trust the nano roller filters (my tank is not going to be "nano", just on the smaller side (56 gallons).
I probably really don't need a roller filter - but I am having issues filtering a freshwater tank, so have emotional baggage about that. I am going to use the roller filter on that freshwater tank first before I move it to it's permanent home on the reef tank (which kind of dictated which filter I purchased - needed a float sensor, not an electronic one). The fresh water tank is going to eat the filter pretty quickly though. Right now, my mechanical filter will clog within 1hr of cleaning it. Water changes, vacuuming, none of that is really helping much - I don't know where all the mulm is coming from (I think 2 fish are active diggers at night). I can vacuum it one day, and plants are being burred by the next. It is also dusting taller plants - defeating my lighting system. I have lost count how many times I have had to clean my filters over the last 2 months.