I first saw this thing and thought it was completely and totally awesome.
After having thought about it, I have parred back my original assessment. It looks like a cool item, but I don't know if it would be worthwhile to have. GPH makes some good points about it's functionality, and you never would have to worry about familiar specific stuff again, but I don't know. My enthusiasm has waned.
That being said, I've only ever donated to the game three times in total. One for my Penguin (don't ever leave me), one for the Flaming Ice Ball thing, and once for the Navel Ring of Navel Gazing that now sits on El Juan and is worth more than I could ever hope to be... So, in essence, I won't be shelling out for this one.
There may be some use for it later, but given that I can pretty much kill anything in one hit or dodge sufficiently in softcore, I'll never need the damage. And I'll probably have enough buffs going on my familiars that using this thing won't help me too incredibly much.
All in all, I'm 50/50 on it too. If I donated more, I might spring for it, but I don't, and my cash is not high enough to purchase one of these things straight out yet.
Tyred