Consider watching Aviation101's YouTube videos on the Sling build. I find it concerning that in the few weeks between shipping the engine and installing it, there were already like 5 ADs on the engine. For example: "do a test on how hard the crankcase is, we made some out of too soft aluminum", or "check that certain oil channels are open, we goofed up and there might be a lot of sealant clogging some", and the latter was the case with their plane. They put in a brand new engine to save time but, the entire engine wire harness is paired to the engine, so they had to remove the current wire harness and replace engine and harness. Sounds like a bleeding edge engine solution. How much more work is on the horizon to keep up with future engine ADs?
I originally wanted to build a sling, but a few key items spoke against it:
1 - Go to FlightAware, and pick 10 random flights from some RV-10s and some Sling TSIs. You will see that for whatever reason, Slings mostly travel at 140 kt, and RV-10s travel at 165-175kt. That's a pretty big difference.
2 - Go to Rotax and check the density of repair shops. If you have an engine problem in a random place, you are stuck for a long time. With a Lycoming engine, you are probably continuing the next day even if you have a bent pushrod and need new valves (own experience at Prescott Az).
3 - Sling uses 6061T6 aluminum, Vans uses 2024T3. Google the difference, or get a sample of both and drill a hole in it. 6061 is very soft but it's probably what they can get in South Africa.
4 - On a Sling, there are no real doors, what opens is the curved window only. You climb in from the top, not from the side. We tried both at Oshkosh before building and the Sling just felt tiny against the RV-10.
To be fair, there are a few downsides to the RV-10:
1 - The RV-10 was designed by Vans in 2003 and they haven't really done much to it since even though it is still one of their two best sellers. If you follow the manual to the end, you have an empty shell. It takes a lot of research to do the entire wiring, place the antennas, place the pitot tube, place the OAT sensor, get seats covered, etc. Compare the build manual to the RV-12 or RV-14, and you will see the difference. There, everything is laid out. Also, the fiberglass parts are better in newer Vans models, for example, the RV-10 cowl has no scribe lines, the RV-14 has so you know where to trim. It also seems, the RV-10 molds are copies of copies of molds, the joggles are hardly present and nothing really fits, so lots of fiberglass work is necessary. This means that you need a good network of experienced RV-10 builders who fill in the blanks. It will be hard to build an RV-10 in a remote place with no-one around to help you.
2 - Even with lots of help, the RV-10 is considerably more work than the Sling to build. The difference can be several years.
3 - Lycoming engines have a long lead time.
4 - The RV-10 has no factory option for installing a parachute like the Sling does.