Dumbbells are a great tool. They help develop increased range of motion and require great strength and stability. If rack positions give you problems ( as is often the case with beginners and the more experienced) they are a great way to get through a WOD challenged with out playing the wrist pain game. Dumbbells are forgiving with mobility issues but aren't too tolerant of weakness. They are also the single greatest tool for curls so you can get some tickets to the gun show. Advanced athletes may want to scale up to 50s/35s or even 70s and maybe a barbell and some different options on the pull up bar.