Radioddity CB Mobile Radio External Speaker, Mini Portable 5W/8Ω, 71" Power Cable, Designed for Car Truck Vehicle

I want to use this with my yaesu ft-891 for pota. i know it will work, but does it make a difference out in the open, such as at a picnic table?

This speaker says it works with db25. i tried it with my qb25, and it locks the transmit circuit open. is there an external speaker for qb25?

Is this speaker water splash proof?

How well does it work with a FT-450D?