The only thing I don't like about Waste Not is that all actions that don't take away durability still use up a turn. For synths with 70 or 80 durability (e.g. anything higher level that isn't a base ingredient) I prefer to use Master's Mend II as soon as it's available. 60 durability restored for 160 CP - and any additional steps I take beyond it that don't take away durability don't matter.
Specifically, if I'm down to 20 durability, and I have 2 turns left on Waste Not, but I get a good status and I want to restore 20 CP from Tricks of the Trade rather than do another quality boost, I'll "lose a turn" with Waste Not.
Whereas if I am down to 20 durability and saved up the CP to pop MM2, I can TotT and get back my 20 CP without losing any turns... because MM2 isn't time based, it's instant.
So while I agree that Waste Not is superior to MM1, I think the choice between Waste Not and MM2 is more of a personal preference.
I also prefer Standard Synthesis as my big completion boost versus Rapid Synthesis, because with Steady Hand II it's 100% whereas Rapid Synth can still fail (I think it's only 80% with SH2.) Yeah it costs 15 CP, but that's a small cost for a guanteed outcome.