I've got them on the secondaries of a Mak and a Dob.
On the Mak (or on an SCT) they are essential, you don't want to fiddle with screwdrivers or allen keys near the corrector/meniscus in the dark with your eye at the eyepiece.
On the Dob they are convenient.
They are easy to fit, but you will lose collimation in the progress (but that's fine, you love collimating your scope, that's why you're getting them in the first place
).
Cheers
Steffen.