But but but...(sorry, I can't help it) , without any signalling you don't know if the vehicle is going to come into your lane early, (probably below matching speed) or take the full length of the slip to match speed.
I'm not keen on being courteous to drivers who don't, (aka, can't be arsed to) signal . If someone signals and it is safe I'll always try to give them what they want. I was raised to have manners.