The higher pitch on the smaller fan on high speed would be more annoying than the lower pitch of the bigger fan on high speed. It's not all about decibels.

I'd say depends on the use case. USB Lithium for more mobile uses, like hiking, One+ for more semi-mobile uses, such as construction.

The 4 inch fan is literally the best fan I have. The 4AH 18V battery lasts for hours and keeps me cool in my room when I'm on my desk chilling.

IMHO Ryobi messed up on their 4v platform. First the battery should not be capped inside the device. That's a part to lose or fumble with, and it's just not a cool design. It should click in like most power tools, or at the very least have a hinged latching door. Also is 4 volts enough for tools? Most seem to be going from 18/20v to 12v for a smaller but still powerful size, 4 volts seems a bit lacking (yes I know power is watts not volts but there are only so many amps one can pull through wires, and why more powerful tools have higher voltages). Will Ryobi make a tool that requires 2 or more 4v batteries to up the power, and make it feel like we are loading an old style D cell flashlight with their 4v batteries? Myself, wanting a more compact design of some common tools I did look at this line as I love their 18v line, and their commitment to not making my tools obsolete by not changing the battery design (and that helps the environment, as I just threw out good tools on another line that the battery is now obsolete, what a waste). But I just couldn't get behind this platform. I did end up going with the Milwaukee M-12 line with a good sale on the compact tools I wanted that in reality was not much more then outfitting those tools fro Ryobi's 4v line.

You can't clamp to 2 X 4

love that accent, eh?