We use Goblets and "sack of potatoes" On a daily basis to help reinforce various elements of both the squat, DL and the OL’s. They are simple and they work.
I think the topic of "when to say when" with regards to allowing form deterioration in a session is very interesting. John Davies (renegade training) Charles Poliquin as a short list insist on PERFECT technique, even in met-con sessions. Personally I think you want to achieve as much output with as perfect of form as possible. The argument that great adapations lie even in the compromised form arena may be true but would output a year, five years and 20 years down the road be even better if movements are curtailed when form degrades past a given point? Not sure and this is the stuff of epic pissing matches but I think it's a very interesting and important point for anyone coaching or training people. Pushing someone to create form deterioration can be instructive and an important part of training. Making deteriorating form THE point of training (faster times, greater loads…) I have not found to be particularly helpful.
"Survival will be neither to the strongest of the species, nor to the most intelligent, but to those most adaptable to change."