Don't get this weapon for the proc. The ratio is great of course, making it an amazing weapon, making it 2nd BiS after Shinai, though I wouldn't waste DKP for this if I already had Shinai + Xegony wraps, since you'll only get about 5-8 more dps out of this weapon over Xegony wraps.
The pet procs about once a minute, and does anywhere from 35 to 830 damage (0-2 hits). Seems to usually miss once and hit once for 435 per proc. A few times did almost nothing, and sometimes (rarely) hits twice for around 700-800 total. This is on a 65 monk with 2 HDEX without pet AAs, so would be a bit better on a BST.
Parsed this thing and the pet does an average of 5 dps total out of my 450ish dps (parsed a couple times an hour-ish). One parse it went up to 7 dps...
So it accounts for ~1% (5 dps) of my damage, so pretty much equal to a DD proc from another raid weapon. Nothing special.