Are pre filters worth it?

Would it even fit on the wr250x/r
anyone use them?

Outerwears Pre-Filter
https://www.yamahapartsandaccessories.com/product/details/pre-filter-by-outerwears?b=Off-Road+Motorcycle&d=20|20

That one doesnt fit its too big but you could probley get it to stay on there if you wanted.

I've used them on other machines, they're great on really long dusty rides, you can pull it off and clean it in seconds just shake the dust out put it back on then keep riding, this keeps your main filter from pluggng up.

They do built custom covers I got the link from them as I asked if they have one for this bike.

Should I stick with the K&N filter and outerwear or use a No toil and outerwear?

It seem that No toil have a cage with a bolt would that fit?
http://notoil.com/products/super-flow-kit.html

They also have the extreme series but could not find it for the WRR.

Stick with a foam filter, K@Ns have let fine dust through on a bunch of people.

IMO K@Ns are fine on street bikes, cars and trucks, any thing that gets used offroad needs a oiled foam filter, they work the best in the worst conditions.