Actually the rationale is simpler: it's more efficient to buy something up front for them and manufacture spare parts. You adapt the items straight away so you

Actually the rationale is simpler: it's more efficient to buy something up front for them and manufacture spare parts. You adapt the items straight away so you know immediately how to repair them, not when a tyre bursts or a motor burns out. From my readings, one problem they had was engineering large permanent magnets which are usually magnetised using induction which is a bastard off the grid. This pretty knocks motor production on the head. You manufacture compressed air equipment with a lathe/mill easily (I've done it and I'm a shit engineer). While I think the religious side is batshit (I'm a rampant atheist), the self-sufficiency model is pretty spot on.