Hope hubs are a very refined, reliable execution of the pawl design. They don't do much to illustrate the disadvantages of the concept that designs like the star ratchet are trying to address.
One potential downfall of pawl systems like Hope uses is that when things go wrong with them, either the pawls or the part inside the hub shell that the pawls engage, which I'll heretofore call the "drive ring" as it's named by some manufacturers, can become damaged. Typically the drive ring is a hardened steel piece threaded into the shell. Some potential scenarios:
- If the pawl mechanism is underlubricated, contaminated, underpowered and/or imprecise, partial engagement between the pawls and the drive ring can occur. In this situation the pawls haven't sufficiently sprung up into the mating teeth of the drive ring at the moment the rider applies drive force. Instead the tips of pawls and the drive ring teeth ram into one another and may slip, potentially causing damage to either or both. Pawl-based drive systems can all do this under the right circumstances, it always has some destructive potential. It's also possible for issues with unequal spring tension, damaged or displaced springs, or other imprecisions to create a situation where some pawls get overloaded and become damaged or fail. Avoiding any such issue is one of the main goals of systems like the star ratchet.
- There can be hardening problems with the pawls or drive ring. Sadly I've seen this on the drive ring once or twice on well-known, expensive, small production hubs, which were at least able to be warrantied. Issues of this sort are of course possible with other designs, but see below why it's painful with drive rings.
In either case, the teeth of either the pawls or drive ring can become chipped and deformed. At that point the problem can begin to build on itself. The teeth have to be sharp for the system to work as intended.
One thing about drive rings is that few manufacturers make them easy to replace if something does go wrong. When it is possible, either you need a new one plus a weird, expensive, proprietary tool that goes in and mates with the teeth, or in some cases you need to send your wheel in to the manufacturer. High-end aftermarket hubs and some wheelsets will typically give you one of those two options. Beyond that, neither option usually exists. You can find some high-dollar wheelsets where once the warranty period has elapsed, addressing a drive ring problem is difficult or impossible.
So while the drive ring is not technically a dynamic surface that's integral to the hub, in practice it might as well be in many cases, and my experience is they can be a little more damage-prone than people realize. Pawls and their hardware are typically more available, although sometimes they can only be replaced along with a new freehub body. And for older, lower end, or OEM hubs, they may be unobtainable.
More aggressive sealing and spring force are both design weapons against engagement issues on a pawl hub ever occurring. (Hope hubs take both pretty far). Reliability is increased at the expense of marginally increasing drag while coasting, the funny thing about coasting drag of course being that to a point, it's not a great concern in most riding disciplines where it's reasonable to split hairs about performance.
Systems like DT Star Ratchet and King Ring Drive, which I'm going to arbitrarily call "drive plate" designs, are trying to make partial engagement closer to being physically impossible, even with contamination and poor lubrication. Contact area is increased at every step of the torque transfer, and it's between two unified pieces, rather than separate pawls that are only as good at engaging all at once as their spring tensions are equal. Extant examples of drive plate hubs make all parts fairly easy to replace but very seldom need it, due to their efficacy at distributing load over more area. This quality is of heightened value in a hub one invests in with the intention of re-using indefinitely as rims wear out.
Pawl systems have an advantage at each approximate price point in the rate of engagement numbers they can obtain while still being reliable overall. At the high end, Industry 9 is a poster child, with ROE numbers down to 0.52°. Plate type systems have in contrast seemed to find their limit at 5-6° for a King or 240, presumably because their torque-transferring parts are smaller by necessity and so making the toothed/splined parts any smaller would sacrifice too much strength or otherwise become impractical.
Another way of looking at is that pawl and drive ring systems, and especially the highest performing ones, need to push everything to the limit in terms of materials, hardening, machining precision, matched spring tension, etc. The best ones are only the best because of how close they fly to the sun. Plate systems don't have that dynamic, but at least as far as what exists to date, they take a little hit on rate of engagement potential.
I personally feel that between the Pro 4 and 350 freehub, both are reliable but the star ratchet design gets there in a way that's more elegant and robust. But, the 8° ROE on the Pro 4 versus 18° for a stock 350 would be a reasonable deciding point. Different riders value ROE very differently, and for good reason.