Keep in mind that if you are entangled, you very likely can't get a knife out from a leg holder, or at least without a fair bit of movement that might tangle you up even worse. This is why knives tend to be shorter now, and stored on the belt or higher, on the arm, upper arm, shoulder straps, etc. Even if you have a knife, those shielded line cutters are too good not to have one: extremely hard to hurt yourself, very easy to remove and to stow, and perfectly designed for cutting line. I have used my line cutter more than 20x, my knife has only been used on dry land.
If you really want a knife (BFK) on your leg, please be sure you can get it out and put it back without doing damage to your suit, your leg, or both. In a drysuit withdrysuit gloves, I would fail this 100%, if I didn't already drop the knife.