Expression of hesitation over second town guide dropping old fake (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

ER (a sound expressing hesitation) before (over, in a down clue) S (abbreviation for second), then A T [o] Z (brand name for a series of town street atlases, especially the original London edition) without the O (abbreviation for old). German-derived word for fake, in the sense of a cheap low-quality substitute for the real thing.