I went with only the pinch-weld adapter (18M-P04) since every car I'm routinely lifting is a VW with pinch weld jack points, and I wanted the ability to lift other cars at the pinch weld- just throw the Renn Stands in the trunk and take them to where the car work is being done. Since they break down into the lifting arm and two supporting legs, they take up very little space in the trunk (or GSW spare tire well), and although they aren't light, they are easily carried and not unwieldy. I debated for a long time about the different systems and investments, but up until COVID it wasn't a concern since I usually use the auto self-serve bays at military bases ($4 and hour for a lift). Once those went to temporary (but ongoing) closure, I re-looked at all the options, including some knock-offs of Safe Jack and a system similar (but inferior) to JackPoint. I would have loved a system like QuickJack, but the (sizeable) investment only helps at the site where it's located, and although with some effort you can move it, it's not really a portable system like the Renn Jacks. I also chose the Renn Jacks because (as we all know) the emergency VW jack is terrible, and IME, although it usually doesn't have a problem lifting a tire off the ground, it's completely unreliable the entire time one corner is up in the air. One Renn Jack in (her) car and one in mine means much more stability in flat tire situations (and using something other than the VW jack helps, too, of course).
I have a few "hockey puck" pads, and have the homemade wooden blocks with pinch channel that many owners have, but each of these didn't provide a system that I could move from MkIV to Mk7 to other pinch weld cars (the wooden blocks are sometimes too wide, too narrow, too long, etc.). I also bought the Renn Jacks when they were on a special sale- seems like a few times a year- for $99+/-, so that helped with the decision. As I said, despite the positive reviews and videos, I was skeptical, but they have good so far. They are not a perfect solution for all situations, but they will allow me to do 90% of what I need them for.