Dynathrust and Master Airscrew Classic 4 propellers are rather inexpensive composite propellers. They do not perform as well as the higher end propellers but work fine for sport flying. Since a converted weed whacker is a sport engine either will work fine.

My preference is the following:

Size 16 x 6 through 20 x 10, the MAS classic 4 is a better performing propeller because it is stiffer than dynathrust.

Since Master airscrew classic 4 are not made larger than 20 x 10, the only choice in cheaper propellers are dynathrust. I have had good luck with the 22 x 8 and 22 x 10.

Hope this helps

Elson