The difference in thickness is more to do with thermal properties, the 4.5mm will be very thin so the cold will come through easier. If its getting heavy usage then thicker will be more robust. I have a car in the garage as well as bikes, when I spoke to garage pride (going back maybe 4-5 years) when I ordered I was recommended sticking with 7mm for a good compromise.
Other brands are available and are probably just as good.
I moved house 3 years ago so took the floor with me and recut a few bits to fit the new garage, so as an investment in a floor, these types of tiles are a good idea imo. Bit pricey but you save on not needing a tradesman to lay the floor and obviously reusable, plus you can make your own patterns with different colours/shades.
If the front of your garage gets direct sunlight make sure you leave the expansion spaces around the perimeter as per the instructions because the plastic expands in heat and buckles if you don?t (yep, I didnt).