I have used the ProRide 598 and its predecessor, the 591 Criterium. I like the 591 better and sold the updated 598 to get more 591s but your experience may vary.

I like these racks because I have fenders on my bike and I dislike constantly removing and replacing the front wheel required for fork mount racks. Then you have to find a place for the wheel. Once you have four bikes on the roof that's a lot of front wheels to find space for.

The 598 ProRide has a very deep jaw that was a design change from the 591 that was needed because:

1. A bike with foil (aero) shaped downtubes allowed a locked bike to be stolen from the rack by unstrapping the wheels and tilting the bike horizontal to yank out of the jaws. There's a good video on this.
2. If you didn't get the downtube exactly centered in the jaw when tightening the jaw the bike could flop out (wheels still attached to wheel tray) while your car is cornering. This usually happens when you have your friend lift his own heavy-ass bike into the bike rack and he's not as familiar with the system. Always check their work.

But since you're considering the newer 598 ProRide what you need to know is:

1. That deep jaw means the bike will need to be rolled backward in the wheel tray while you swing the arm into place and tilt the bike frame into the jaw opening. Then you roll the bike foreward into place when you get the arm right where it belongs.
2. There is only one place where the jaw belongs where it clamps the downtube and it is based on the geometry of your bike. The placement of the wheel tray clamps is determined by this. The wheel tray clamps are easily slid to adjust to different bicycles.
3. Very small frame bikes, mountain bikes, and bikes with waterbottle holders will have less maneuvering room inside the frame triangle for getting the jaw into place. With each new bike you put in place you're going to have to learn how to get it in there. More easily done with a second person helping hold the bike.
4. The fore and aft placement of the wheel trays in relation to where they clamp to the crossbars can be adjusted and can only be done with the system off the car. Start with the default placement, it seems to work pretty well.
5. If you want 3 or 4 bikes then alternate bikes facing forward or backwards so handlebars don't interfere.
6. I mentioned rolling the bike while swinging the clamp in place. If you have two hands, one hand will be holding the bike upright and rolling it back and forth while the other hand positions the arm and clamps the jaw. If that sounds tricky and fraught with peril, it is. I'm 6'2" and have been using roof racks for 30 years and I could not get the hang of it over the course of a week long tour where I did it 8 to 12 times every day. (4 racks).
7. If you have a friend, have him hold and position the bike while you position the arm. This helps a lot.
8. The wheel tray clamps don't hold the tires very deep into the clamp. This makes heaving the bike up into the trays tricky; the tires bounce out easily.
9. The wheel tray clamps have a strap that goes diagonally over the tire rim. This strap must be unclamped and out of the way before you lift your bike off the ground. Forget and you'll be lifting that bike up on the roof twice.
10. After you remove the bike the straps are unclamped and ready to receive the bike later that day or next week, right? If you drive anywhere the rubber thingy on the strap will fly off never to be found again. When you unclamp a wheel there is a slot you can put the free end of the strap in that will preclude thingy loss. Get in the habit of always putting it in there as it also avoids the aforementioned double bike lift.

These racks are meant to be operated at eye level and if you're a tall person with a regular size sedan or a regular size person with a low slung car it works pretty well. If you're putting the rack on top of a camper shell you're probably going to need a platform to stand on and someone to help you.