I have a 4500 and a 7.5fx. I ride the 7.5 to work on rough roads, gravel and grass with no problems. I use the 4500 when I mountain bike (not often) and really don’t care for it much. The components are crap. The derailleur hesitates when sifting, the brakes suck and the crank arms fallen off a few times. But if you inflate the tires you can get some speed on it. I loaned it to a friend who hasn’t biked for a while and he kept up on a 15mph average, but exerted a lot more energy doing so. I got a great deal on both bikes and had to take them. The 7.5 was 500$ and the 4500 was 350$.