The spark arrestor is a screen, often cone-shaped, that is required by US Forest Service and most states to use a vehicle off road. It keeps flaming carbon from puffing out the muffler and starting a wildfire.
I choose to use a spark arrestor. The chance of a KLR starting a fire may be small, but I've fought wildfires and they're no fun.
It won't be a major help for backfiring or popping in your exhaust. It may make the engine every so slightly richer which would help if it was right at the edge. If you have popping or banging in the exhaust it means that the engine is running lean. Which leads to . . .
You will probably need to rejet your KLR if you put on a freer-flowing exhaust. Some come with recommendations, some don't. My KLR came with an aluminum muffler and ran way lean. I put on a stock muffler, AND a smaller main jet (& KLX needle).