I am unsure of what we are talking about here. The only Sure-Fire magneto replacement I could find is from a Pazon Ignitions Limited out of New Zealand who design magneto replacement electronic ignition models for European motorcycles. When they're not sheep farming. I could find no reference where anybody has adapted those to experimental aircraft, either via Google or here on VAF.
Meanwhile, Kelly sells both Slick and Bendix overhauled magnetos so I don't see where Kelly and Slick are different products. For what its worth, all else equal for conventional magnetos I would take a Bendix type any day over Slicks, if only for the quality of the internal parts alone. Taking them apart to do a 500 hour inspection can be revealing. Magneto mechanics tend to prefer Bendix too based on what they see. But both brands are fine and seem to work fine.
As far as the log book entry a single sentence "inspected" would yield the same concerns to me. Magnetos should get a "500 hour inspection" which is more than just a look over. The casual observer would expect the word inspection to mean just take a good visual look. Nope. In the defined 500 hour inspection process magnetos are stripped down and inspected and then certain wear parts are replaced like bearings, and points and condenser. Rotors and capacitor are usually kept in service if in good shape. Slicks don't fare as well and usually need something like one of the plastic gears replaced and they cost a bit more than Bendix because Slick doesn't kit an inspection parts package, they charge piecemeal for every little part.
Meanwhile, like Ed I have been running a single SureFly magneto replacement along with an original Slick in my Husky for two years. Neither one are new type needing to be beta tested. I am not clear on which of the two (or a Pazon Sure-Fire) would classify as being a beta tester.
On type certificated aircraft, when Slicks need a 500 hour I try to core them in for Bendix (or CMI or whatever they call themselves these days) compact series magnetos. They're good stuff. A.E.R.O. In Stock used to be a great source for the CMI compact magnetos and would be very lenient with cores. Unfortunately they got bought out by Aircraft Spruce so effectively disappeared. So now it's back to the clueless customer service reps at ACS.
On experimental aircraft I have been very happy with dual Pmags, Bendix conventional mags or a mix with Sure Fly like in my Husky. Not that I am dissing the more advanced and modern EIS/EFI aircraft systems. I will be up for trying one when the opportunity presents itself.
If by chance the OP was referring the SureFly instead of Sure-Fire as alluded to, the impulse magneto is a popular candidate for replacing with a SureFly unit. That's probably a good way to go on an RV. On my Husky's angle-valve 200hp Lycoming I opted to keep the left impulse mag and instead replaced the right non-impulse mag with SureFly. This required removing the grounding jumper from the ignition switch to get both ignitions to fire on start. While I realize keeping the left mag leaves me with the troublesome mechanical impulse coupling, here is my reasoning for it. They Husky mission profile can find that airplane alone in the back country without help. So if my battery dies for whatever reason I can still hand-prop the engine on the left impulse magneto. Then the SureFly internal dynamo power will kick in at some higher RPM. Also, hot starts on the injected Lyc can be troublesome and so I wanted all the spark available (8 spark plugs) up and helping start. If the Husky was ever on floats this is even more important because after pushing off the dock the aircraft drifts with the current until the engine starts giving thrust to the pilot to gain control. You don't want to be doing a failed hot start sequence as you uncontrollably drift towards a $2M Cessna Caravan on floats or into the rapids. For daily float flying a carbureted engine is probably a better choice. But that's not me but I think having 8 plus firing helps a lot with hot starts.
By the way, the only difference between the SureFly model designed to replace impulse mags and the model designed to replace the non-impulse mags is the mounting surface and gear. So SureFly makes sure you don't have to buy replacement mag gears depending on which mag you replace. It's a nice touch as compared to the likes of Pmags which require the aircraft owner to buy a new non-impulse gear if replacing the original impulse mag. So SureFly can save the gear cost over Pmags.
