This is a good idea. The SippiGrip is basically a tether for your sippy cup (or toys or whatever you don't want to fall on the ground). It's a piece of fabric that attaches to the sippy cup with velcro at one end and attaches to whatever you want with velcro on the other end.
I have several of these. I put one on the high chair and one on the stroller. We always take one when we go out to eat. It's so much nicer to have a meal when you aren't retrieving a thrown sippy cup every thirty seconds. Also the sippy doesn't hit the floor and get all dirty and yucky. The tether can be adjusted so that the cup is in comfortable reach for the child.
I have read a review of this product that says it can be a choking hazard. I don't know how that is possible (and believe me, I did try to figure it out!) . The tether really isn't long enough to wrap around a child's neck, and hopefully you are supervising the child anyway.