My rule of thumb. Don’t warn the girls you are about to cum and just do it. Unless they tell you before their session what they don’t like (which I never ask), if I’m getting head and about to bust, I just let it go.
In regards to Britney aka Thanos aka Ruth from Red Velvet, my experience with her has been great. I’ve seen her 3 times for the hour at Red Velvet and it was always a CIM finish, no extra tip. The sessions was very GFE and she always did what I asked. I guess ymmv.