I've always been using a couch or a bed frame or whatever to anchor my legs, but it makes so much more sense to use this piece of equipment. It really helps build consistent form when doing sit-ups.
The big issues though are the following:
• The screws that come with the equipment are not long enough. I had to go to a hardware store to buy separate screws that were long enough to fasten tightly to the frame. The other issue with this is it bends the metal lip where the nut is soldered due to the additional force. Not exactly great design.
• The suction cup is a little hard to actually find the right grip. I've found that if I spray/mist the bottom with some water it works a bit better, but it shouldn't have to. The cup itself is pretty thick and I wonder how effective it would be if the edges were a bit thinner so it replaced the air a bit easier. Not sure though.
Overall pretty solid once you get it to work. Getting it to work properly though can be a bit of a challenge at times.