I have S. repens in my moderately planted, low-light, non-co2 tank. It's my low-tech solution to carpeting plants.
They grow very slowly, so don't expect them to start multiplying for a couple of months or more, depending on your lighting etc., but they should root themselves in a couple of weeks.
And yes, they are very difficult to plant. What I did was just start planting them in clumps. Over time they will be uprooted a few times, and they split apart on their own at the same time. Just keep planting them back in and eventually the roots will take hold. I have sand substrate, so mine took a while, but they are definitely rooted well now.
Their roots are actually quite strong and the plant is nice and hardy IME. I didn't have any melt at all when I planted them, while nearly every other plant I got melted at the start.