We have a mifold, and it tends to float between cars as needed when friends are along. It's good for one-off needs, but a bit of a pain to use, so not great for regular use. Essentially, the problem is that it's too portable, and doesn't stay put when not in use.
Well, thanks to this specific thread I bought two mifolds and the kids absolutely love them. Much smaller and it took about 5 minutes and just a few tries to teach my 6 and 8 year olds to strap in on their own. I didn't fully understand how they worked from the product website, so I made a video: