Quote from Friggerton;1184674:
http://wiki.mabinogiworld.com/view/Focused_Rainbow_Beam_Sword
I'll probably be using one of these with my elf - though it can't be upgraded/special upgraded/enchanted it already starts with a pretty high min-max. In my opinion it'd be nice to have a fairly powerful weapon you don't have to chase down enchants for, but that might just be me. Also doesn't take terribly long to save up the seals if you have multiple characters and know how (I net ~28 seals a day with 4 characters with just life skills, so my daily total is usually closer to 35)
Beam is a great beginner weapon thanks to its stupidly high base damage.
However, it's not worth the seals. Better to save up for Royal Knight Armor and profit. Just save up on money and buy the sword, although I'd really recommend them on humans than elves, since there's really no point of beam swords besides dual wielding.
For Giants though? Clearly not a good weapon. As it is a "one-handed" weapon, it won't get the smash damage bonus that you'd get from 2h swords (yes Giants can equip it with shield, but the multiplier is still considered two-handed, since the weapon itself is classified as a two-handed weapon.). Special upgraded two handed weapons easily surpasses beam swords, not to mention superior reforges.