Houdini clip

[frustratedpants]

Not sure where to post this but here goes..
Does anyone use a Houdini clip? If you do, how easy is it to move? As in can you slide it down the straps or does it just stay where you put it?
Dd can generally get out of anything, and don't want to waste the money if it's not going to hold her.

I have one, but have never used it! Its kept in the car in the car seats after one horrendous tantrum from DD. I will have a look if I get chance. I have another version too but I dont know where it is. But I got it from Amazon. There is an expensive version available to buy which is a fabric that stops a child putting their arms through. I looked into buying it a few weeks ago as DS has started this trick, but all the reviews / messages said to check the seat harness straps first - they were fine - but I think our issue is that the seat is slightly reclined and we don't take this into account when sitting him in. I am very wary of adding anything on because its such a grey area on car seats but obviously isn't the same safety risk on a pushchair.
Have you tried a food clip or does that just slide down? Have you added on another harness with the buckle backwards to the D rings?