Everyone’s design varies slightly, we use a #3 REC Thorne and DH use a #2 ( I believe ). The difference is quite small, if we are comparing outside guides to outside guides.
Fly guides are good, but they are not very durable. They are heavier which will slow certain rods action. The noodle rods are where REC really are needed.
REC have a smaller surface area so water does not have as much area to freeze on. Like everything eventually you will get freezeups. They flex inside a rod case as well.
They are not cheap though.
I have used fly guides on ice rods for years the benefits of REC for ice fishing is well worth the $30 in guides IMHO.
John