Meh - I was pretty happy merc won - I think I dislike max/Redbull more than I do merc/Hamilton (just). And he overtook on track ***.
Is it just me or did merc hand verstappen fastest lap (or a very good shot at it) again? As soon as they pitted bottas they handed max a free stop if he got overtaken. They nailed Hamilton’s strategy to win but bottas is just dead weight at the moment - he nearly took Hamilton out by not moving over and can’t get anywhere near fastest laps. If it were my team Russell would be in now.
For trials use it is mostly personal preference. 170 is stiffer and lighter just by way of lever length and your legs travel a shorter distance per revolution. 175 offers greater torque, but might not fit some trials frames or rub under hard kicks. Whenever you find yourself debating 170 vs 175, just remember Charlie Rolls uses 165s.
Chains are a hot topic of late. You said it yourself, you should change the chain at least every 6 months if you actually ride. Every 3 months isn't out of the ordinary. Chains are very reasonably priced for what trials riders need so there's no reason to skimp on this. I cannot stress enough that breaking a chain while riding trials can be a LIFE CHANGING experience.
As for chain stretch, I have one of those things too, but I change my chain before it tells me I need to. They're nice for multi geared bikes and people who only ride occasionally because a stretched chain will ruin your drivetrain; multi gear or single speed. If your drivetrain includes one of those expensive Inspired 22t with integrated bash, you'd much rather replace a chain twice a year than one of those every year (plus the chain!)