john_johnson75 basically said run em til they give up the ghost which sounds about right honestly. that $40 sharpener is probably the tool equivalent of those "as seen on tv" knife sharpeners that promise miracle edges then just chew up your steel. i bet the diamond grit on those things is uneven as hell so you're basically giving your bit a lopsided haircut with a dull pair of scissors. if a bit is so dull it's burning wood instead of cutting it then yeah maybe look into a proper sharpening service but for most hobbyist stuff just crank up the feed pressure and buy a new one when it really dies. better to waste $20 on a new bit every couple years than risk trashing a perfectly good one with some amazon gadget.

Dude, my friend swore by zip ties until he had to cut one off and nicked a wire.

Oh man, Ive been there with wonky walls, it's the worst. Seriously, @white.grant you're totally right that those cheap speed squares cant handle real world problems like crooked plaster. I had an old house where the corners were at least a degree off from each other, and I almost threw my square out the window trying to make sense of it. Its such a simple tool thing but it makes a huge difference in the finish. Solidarity from someone whos been fighting the same battle with a stubborn framing square.

So is the gauge actually accurate or just close enough? I've had cheap pumps that read totally wrong but still work fine otherwise.

Yeah @the_hannah is right, is it really that deep though?