Size comparison

Although very wide Jump Blocks over 65mm look a bit too chunky in my eyes, but it's a good solution if you don't want to put your feet quite close to the shell for whatever reason.

For such cases, the block is not only wider, but depending on your requirements, it can be ordered a little larger in diameter in the lower part, and also a little thicker.

This prevents the foot from sliding closer to the shell.

What size should I choose?

Actually 65 mm, because it is the standard size for a reason and is usually perfectly sufficient.
It's wide enough to reach over the middle of your foot without your foot slipping past it when jumping.

Narrower than 65 mm only if you want to have it more discreet and accept a little less contact surface.

Wider than 65 mm only if your feet are not close to the shell. For example, if the legs are too short and / or the wheel is too wide and the wheel presses against the inner thighs and for this reason you stand more on the outer edge of the pedal.

The Jump-Blocks should only be as wide as really necessary.
A wider block means a higher leverage arm on the base plate, which in the worst case can lead to a faster breakage in the next crash.