Where do you get the bad reports on Castrol? I've used it for years in everything with excellent results. I do use Mobil Racing 4T in the TBird and it has done a great job, but I see Triumph is now recommending Castrol instead. I can't imagine they would do that without serious testing and a good reason to do so.
I've read more negative things about it than most other oils for years. But you gotta understand that you can probably run the worse oil and not break down. Your bike may degrade in performance over time w/o you recognizing it, or it may break down at 100k. Not that you will necessarily take it that far, but the point is you can run any oil w/o noticing anything. Look at what i said i read about motul, yet people generally consider it very good. Maybe its wrong, but maybe not. Point is like i said you don't put lousy oil in your bike then start it up and it breaks immediately or runs like utter [email protected]
Triumph recommends whatever they get a good deal on. If M1 was still offering the same cost as castrol or better you can bet they wouldn't have changed.
Anyways, i'm not saying it's going to let you down. i'm just saying you may feel a beneficial difference. I did and it was very noticeable so i'm simply giving you food for thought. Whether you want to try it is your call.