I have no idea what I meant, sorry. I've been using Jenkins for a while, and have cobbled together something that works, sort of. Short version is I had to use a sub job so I could run on a different host than the parent job. (Very long story, I'll leave it for now).
And, as you say, my example failed, so I switched to yours, and it works great, thank you.
Given that the jobs we run tend to run for HOURS, if not days, I'm not very concerned about performance unless its something really bad. This command will get run no more than 2 times per stage, and a day-long run has maybe 10 to 20 stages, maximum.
I am, however a little concerned about the 'other issues'. If someone can point me to where to find issues (indeed, documentation! - I'm still struggling to find things) - I would be grateful and will go off and read.