For very short weapons, like a cestus or a dagger, it's by-and-large true.
For mid-sized weapons, like a rapier or a staff, it's true only if you know that specific weapon very well: grab one which is 10% shorter or longer than what you are used to, and you are bound to make mistakes.
For a long weapon, like a pike or a lance, seeing the tip of the weapon makes a whole world of difference, trust me.
Furthermore, if you are fighting as part of a group (unless it's one trained to fight together with invisible weapons), an invisible weapon makes it far easier for your mates to get accidentally in the way.
You don't need a Finesse roll to have a person look and sound an exceptionally authoritative "special person". What's so different with the stew?
I entirely agree and scanned before saying something similar, emphasizing that you don't need to see your practiced and familiar personal weapon, but you need to see one you don't know. You'd adapt quickly to an invisible weapon you're not familiar with, but it takes at least a little practice.
Oh, for goodness sake. Just design the spell so it doesn't destroy the visual species that the weapon emits in the direction of its wielder; to everyone else it'll be invisible.
Neither of the spells in the "Transparency Examples" sidebar of Houses of Hermes: Societates (p64) have a +1 magnitude for Complexity (nor a Part target), and they both selectively destroy all of the species emitted in a particular direction.
Those examples on p64, the first has a higher Base to account for the shifting of the direction. This is clearly stated in the write-up. The second requires Finesse rolls.
So the first basically has +1 Complexity (just added to the Base) and the second requires a Finesse roll not to have that +1 Mag.