Sash windows

[Gloschick]

We own a Victorian house. Most windows are sashes but there are a couple of windows which are dodgy 70s replacements that we would like to put double glazed sashes in.

The design would be 4 panes. The options are either to have 2 windows with a stick on bar, or 4 separate double glazed units. The former would have a better appearance (because a thicker bar is needed with the latter) but the window guy says that it is more expensive/hassle to fix if the double glazing fails. Does anyone have any experience in either type?

The ones with the stick on bits are easily broken off if you accidentally use them to open the windows with, also make sure they do a proper weights and pulleys system. The spring things are really crap, look awful and are really difficult to open and close.