We have a 2015 X5 diesel. Using information from users on this site and other sites, I added an invisihitch to the car when it was new.
The hitch is nice in that you can remove the draw bar when not in use and the hitch cannot be seen. The only limitation with the hitch are the ears for safety cables - they are small and close to the hitch and so have little clearance for hooks. I use D-rings rated for the weight and then connect the safety cable hooks to those.
My trailer has electric over hydraulic brakes and so requires a brake controller in the tow vehicle. I purchased the BMW version of the Tekonsha brake controller kit with its long cable. Rather than install the controller permanently, I just plug it in in the rear, run the cable between the seats to the front, and mount the controller in the a cup holder for those few times I pull a trailer with the x5.
The car pulled my 18 foot boat great (about 3500 pounds max). It also pulls my 23 foot boat (about 7500 pounds max) OK - the x5 has plenty of power and braking ability but the rear suspension is a bit soft for that weight and sits near the bottom of its travel.
I towed only short distances like 10 miles over local roads and never got above about 45 MPH. For the lighter boat I would have no hesitations taking a long trip at highway speeds. For the heavy boat I would not want to take a long towing trip.
I have a Tundra truck for normal tow duty, but it is nice to have the x5 as an option.