What brand stacker door/windows did you get?
went with Rylock. Mine isnt glazed yet either - and im still struggling! its bloody heavy. I think it will be good because when double glazed my kids wont be able to open it.
Rylock make some nice windows.
I disagree that being heavy to open is a good thing. If it's heavy/difficult to open it means that the rollers aren't rated to handle the weight.
I'm not sure what the total weight of my sliding door will be but the each pane of glass will be approx 200kg. However the door is still easy to slide as the rollers are rated at up to 300kg. I went for a uPVC lift and slide system.