Also, I would prefer to employ a plumber who runs a nice clean length of piping in the loft and fastens it down properly, or who explains that they'd recommend

Also, I would prefer to employ a plumber who runs a nice clean length of piping in the loft and fastens it down properly, or who explains that they'd recommend an approach that's a bit more expensive because it's more long term reliable, and so on. This kind of thing is a sign that they actually care about what they're doing, and suggests that they're less likely to, for instance, forget to actually properly complete a connection so that the next person who bangs into that pipe causes it to break apart and flood the place. [That last happened to my parents the other month.]