I like it for the simplicity, and it's a bit more forgiving than a real SS/FG, same level of complexity with very little weight penalty. If you consider a range of 60 to 100 rpm, you get quite a wide interval. I have double in front, 32/28, and double in the back, 18/14, it gives all together 12 to 30 km/h range. No need even for a second chain link.

When i have to portage the bike i can tell there is some difference in weight compared to properly geared bicycle.