Should flex tails be replaced when fitting a new mixer?

If the old tails have already served for years, yes. A new mixer on old hoses is a common cause of pointless return visits.

Can an expensive mixer be fitted onto old crooked wall outlets?

Sometimes yes, but not always neatly and not always reliably. The outlet geometry and thread condition should be checked first.

A small residual discharge from the spout can be normal, especially on high-spout mixers. Continuous dripping is not.

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Mixer installation in Israel — kitchen, bathroom, shower, connection and prices | KABLAY