What do people think of these frames?

Off the peg.

From experience a few layers of lacquer will not be enough to protect it especially if you use it throughout winter.

What does off the peg actually mean? Not mass produced?

By protecting it do you mean: preventing rust and the bike collapsing from under you?
I keep my bike inside most of the time. It's only really when riding that it gets wet. Winters almost over anyway. The beasts from the easts are getting less effective.

Is there anything else one can cover the metal in other than lacquer? Some kind of transparent anti-rusting agent?

Best wishes