I had that happen years back and I will not buy a bike without one. Especially since my next bike will be a C2W from Halfords![]()
The bike snobs would call it a "pie plate" and ridicule you for still having it on your bike, and treat you like a social outcast and probably refer to you as a dork.
I personally can't see anything wrong with it and it does perform a valid function (albeit a mostly redundant one for correctly setup bikes).
I still have mine attached and couldn't care less what people think about it.
Why do people take it off when it could save you a fall, chain, some paint etc..?
But will the mech need adjusting or not?
You are putting an identical cassette (just one which is a little lighter); if you never experienced the chain going into the wheel before you will not require new adjustment.