The new big hide at Titchwell Reserve in Norfolk is superb. It has glass panels which can be raised or retracted, so birders have the option to view with or without the glass. No problems there, everyone's happy.
Going back to BMW, Rob72 is right to point out that the reception / viewing area occupies the prime viewing location on the site - and it's entirely glass fronted ( and double glazed ) If there was an adjacent viewing room at the same primary viewing point which offered a non obstructed view then I wouldn't have a problem.
And finally, why are there fixed glass panels as well as open windows in the new Covert hide at BMW. What's the thinking behind that ( I'm genuinely curious )
a) Titchwell cost a LOT more
b) Reception occupies a excellent viewing spot, that's the point.
c) As stated a few times there are several alternative viewing locations outside of the glazed areas AND other viewing facilities are in the offing
d) The fixed windows in Marsh Covert Hide are for exactly the same reason as Reception, to allow instant panoramic vistas, be welcoming/familiar to non-birders and the view the sky (I love a raptor watch I do!). The hide was also designe dto accomodate more than just seated birdwatchers, you can stand behind a seated person with your scope/bins
e) great views of juvenile Marsh Harrier this morning from reception.
f) 2 great white egrets came into roost last night ... viewed from the marsh covert hide