More power to you, it's the beauty of the 919, we can do with it what we will.
Though I'll say a few things. $100 is definitely worth it to not feel cramped on a bike. If you're not a tall rider and just looking for fun mods, I agree, better way to spend $100. Second, just like with anything, it's as strong as the weakest link. These pegs only add one more "part/piece" than the stock setup. It comes with blue loctite already on the bolt, an extra tube of thread lock for the overkillers out there, and redundancies like the holding pins. Properly torque it all down and you're good to go. Plus this isn't an ADV bike, our weight is on the seat much moreso than the footpegs.
Just my 2 cents for any readers of this thread looking to make their 919 more comfortable because of knee problems or long legs!