I agree, the OO market is quite saturated, with manufacturers now producing the same prototype as well on occasion
with the new scale TT the world is your oyster
Taking the class 31/Brush type 2 as an example, not only do you have current production you also have 50 odd years of previous examples still around to compete with
On TT 120 you are the only game in town and there is no cheap second hand stuff knocking around either
You may also be one of the few diesels around to choose from for a while