There was a thread here previously about the BMI business class and comparisons, so you might want to try searching this forum.
I last flew business in October, from MAN-ORD on the A330, which I believe should be serving the LAS-MAN route but someone should be able to clarify this.
While the seats aren't the latest, the service and food are notoriously good. Business is the highest class of service on their flights and so the service is very good normally.
That said, you might want to get the opinions from people who have flown more recently, as my father flew very recently and said that he wasn't as impressed as before although this could have been an exception.
Thanks