The PVS-30 and PVS-24LR have approximately the same overall performance. Each has its tradeoffs; there are more lenses in the optical path of PVS-30, so more light is lost going through the layers of glass than with the mirror system (catadioptric lens) in the 24LR, but the catadioptric lens on the 24LR is smaller, so less overall light can enter. This tradeoff results in the image intensification being about equal between the two. Refurb 30s are less expensive, but typically have older, lower spec tubes - ~1800 FOM GP for the 30 vs ~2400 FOM WP for the 24LR.
Practically, the darkest dark nights require supplemental IR illumination for both clip-ons in order to see long distance. On a moonless, cloudless night with some sky glow, I've been able to just barely make out an IPSC target at 400 meters against a high contrast background with a PVS-30. Moonlight significantly improves the performance, with 1000 meter shots being possible under a full moon. As an aside, supplemental IR is not a bad thing to have, since it enables you to see mirage and trace in total darkness.
Each clip-on can potentially be retubed - Jay at Sure Shot Night Vision has the knowledge and tooling to do both the 30s (extremely tricky) and the 24LRs (less tricky).
One significant difference is in the tail end of the optics, where the Risley prism sits. The 30 has a shorter tail section, which translates to a larger tolerance for angular misalignment with the day scope. That is, if your scope is on a 20 MOA rail, but the clip-on is mounted to a flat front rail, then the 30 experiences less POI shift (in my experience, none) due to the difference in angle between it and the day scope. The 24LR, on the other hand, has a long tail section, which makes it more sensitive to angular misalignment, so it should be mounted in the same plane as the day scope - either on a continuous rail, or one which is at least parallel to the day scope rail. Both clip-ons tolerate being offset horizontally and vertically.
The difference in the lengths of the tails can also make a difference in whether the clip-on fits a specific rifle. A long objective bell scope combined with a short chassis can leave too little space to fit the 24LR.
Finally, it is technically possible to adjust the 24LR's collimation, since a Risley prism adjustment mechanism is accessible by removing a small rubber plug on the tail end. Do not try this if you don't have the correct optical equipment to check the collimation - that's a great way to void the warranty on a very expensive piece of gear. Conversely, the Risley prism of the 30 is epoxied in place.