In my opinion those prop and skeg protectors are gimmicks. Invest your money in a good ff/depth sounder that reads at all speeds.
Respect the river. If you're going to run a prop, your going to hit bottom once in a while, they key is not to do it at full speed. Watch the depth all the time, as the bottom starts coming up at you - slow down and take appropriate action like heading for deeper water.
Pay attention to the river bank - a steep bank normally means deeper water - but not always.
Shallow water is normally associated with the long shallow slope beach - mind you no beaches right now.
Watch for the ripples where you think there are islands.
Experience and familiarity with sections of the river will give you confidence in safe passage.
Back to the guards, you'll spend $100 on one and if you do hit something you end up bending that guard into your prop or breaking off your skeg. You also loose power due to increased drag - enough that you can feel it.
A stainless steel prop will give you longer life if you run the prop through loose pea gravel or sand and will withstand a lot more hits than aluminum props.
Nice thing about the high water expecially once the freshet starts to taper off and no new trees come down the river - lots of room out there.
Just respect the river and use common sense until you're confident on your route.