I imagine that on most bikes the Chainglider "arms" will need to be shortened. Finding a bike on which either factory length of Chainglider fits out of the box would be mainly a matter of luck.
I was lucky on my first 3 Chainglider installations - 2 large Thorn Raven Tour frames and an old 650B frame with reasonably generous clearances.
No shortening of the Chainglider needed, but I did need to remove the red button on the rear part of the Chainglider on the 650B frame to prevent the Chainglider from rubbing on the seatstay.
4th and 5th installations needed shortening. Both these bikes were small "ladies" frames - the Raven 390 step through that I am currently building, and an old 700C twin-lateral frame with fairly close clearances for 28 mm tyres.