Summary: This works very well. When not in use the legs screw up into the monopod. When they are retracted the same screw locks them into the down position. This provides a quite stable quasi-tripod. I wouldn't put a very long very heavy lens attached to a camera body and expect great stability in a wind, but for augmenting the monopod, the device is great.
Summary: I bought this hoping to have a relatively small and stable platform from which to shoot low light when travelling. The problem is that these legs only really provide a stable platform for long exposure (> 1/4 sec) when the monopod is closed. With only one section extended it wasn't bad for 1/10 to 1/2 sec, but even then I had some shake if I wasn't really careful. I put the legs on my 680B with the tilt head (3239?), and the legs almost doubled the weight.
Summary: i love the versatility of this foot. when i dont want to lug around the tripod, i use this foot. its not completely stable for long exposure but works in a quick bind. it is sort of bulky at the bottom and it does get considerably heavier.
Summary: I added this folding base to my trusty, old Manfrotto 479B monopod primarily to support my camcorder while shooting stills with my Canon 40D. This setup allows me a simple, hands free video recording solution with the freedom to fully use my dSLR - getting the best of both worlds for those great family events without having to juggle two devices!
Pros: Easily Adjusted, Good Footing, Lightweight, Locks In Tight, Rugged, Smooth Movement
Summary: I have used the folding base with a landscape lens and a 100-400mm IS lens. The folding base does help steady the mono pod. It's easy to fold the legs inside the mono pod. However, I work in the field most of the time and the legs pick up mud and grit. A have a box of tissue in my vehicle to clean the legs. I would recommend the folding base for those needing added camera/lens support.
Summary: I have not "road tested" the base yet but it appears to do exactly what I needed it for. I purchased it because I often find myself in a situation where I can't use a full sized tripod but wanted more stability than a monopod provides. This unit gives me the flexibility to use a monopod and still get the extra stability when I need it. It's a bit more heavy than I had anticipated.