It depends on the lounge. The one upstairs (Gate 16) is good. It has its own toilets, a pretty extensive buffet and natural light on account of the windows with a view over the apron. Gate 4 is rubbish. You'll always get in with a LH/SN flight.

Next door, you can visit Plaza as well.

Compared to GLA's Upper Deck, where the better Lomond Lounge has permanently closed (which was pay-in or £15 extra on Priority). It's a paradise.