Mecanum wheel is also called the Swedish wheel or ilon wheel after its inventor , Bengt Erland Ilon. Unfortunately this sharp mind is still a hidden person as there is no data or photograph of him on the internet. Mecanum wheels are extremely useful for tight space crunch and are a horrible choice for cars or motorcycles. I will tell you why.
There are two major downsides of the mecanum wheels, one being the weight these wheels can handle and second being the traction! In the video at 4:45 for forward motion the wheels cancel the X components and Y components combined. And so the X force components are simply wasted. This is why for our cars and motorcycles where forward motion is a crucial aspect, mecanum wheels are a horrible choice. But for a cool sideward and rotational forklift this is the best.
And yes there are also some smaller downsides like complex arrangement as there are many tiny rollers, etc. Due to this the manufacturing is difficult as well!