Lots of restaurants have always had 2 for 1 on main courses, 50% off on them etc. on Monday-Wednesday anyway 'cos they're such quiet days and this offer is barely more than that
I could actually see the 50% off as ending up being worse value than the usual weekday deals in a lot of places because it's limited to a tenner. Unless, of course, restaurants still do their own deals as well as the 50%.