I have many locos (HO) that have flywheels and many that don't. The difference in performance is very great. If for some reason the track power is cut the locos without flywheels slam to a abrupt stop while those with flywheels (most of them at least) coast to a stop. When this happens on my layout (rarely) it's always on the back side and on a curve, the abrupt stop causing cars to derail.

Here are some links to the Ring Engineering EOT device in the Walther's website.

http://www.walthers.com/exec/productinfo/634-EOT33

http://www.walthers.com/exec/productinfo/634-EOT36

http://www.walthers.com/exec/productinfo/634-EOT33LW