Final flash may take up awhile, but once it passes the first yellow line its still pretty powerful. If your setting up a powerstruggle, then chaarge tiem doesnt really matter, but if ur trying to block a beam commin towards you that isnt generic and your not charging it, i suggest blocking couse a kamehameha cant even do that. But if you mean ur charging a final flash and kamehameha shoots at full power and your not charged all the way, it will still put up a fight depending on the opponents power level, cuz if you put people of the same power level and have a kamehameha v.s final flash power struggle, chances are final flash win cuz like thr other guy said, Vegeta is dangerous.
::Edit::
Sorry if this is off topic, but "beam spammin" and "melee spammin" have 2 different qualities. Beams are just for the love of blowin things up, the colors, the simplicity, and power struggles....And i must agree thats a hell lot of fun. Btu when someone use melee, they are usually just looking for an intense and fast play or to better themselves becuases melee is usually used to deterimine one's skill in the game, unfortunatly.