Dee Elliptical Curved

Stainless Steel
Prevents pinching corners of mouth
More control with steering
Reduced nutcracker action
Curved mouthpiece is more comfortable

A dee ring snaffle is a cross between an eggbutt snaffle and a fulmer snaffle.

It is less bulky than an eggbutt, prevents pinching at the corners of the mouth, and has more control as it has longer cheeks/shanks than an eggbutt.
Because of this degree of control and safety, this bit is mostly used in show jumping and racing.

The dee shanks are longer and straighter than an eggbutts, so the bit works more on the sides of the mouth, giving the rider more control with steering, without the bit being able to be pulled through the mouth.

The oval elliptical link is basically a variant of the French link, with a rounded lozenge instead of a flat spatula joining the two halves of the bit.
The benefits are largely the same, with reduced nutcracker action, more even pressure over the bars, and independent control over the two sides of the mouth.

The curved mouthpiece creates more room for the tongue, making it more comfortable for the horse.