Yup, that's the stuff. Milbemycin oxime is the active ingredient.
One large dog tab contains 23mg of m.o. and is sufficient for dosing like 380 or 390 gallons. I used a razor blade to cut the tab into quarters to dose my 100g.
Typical instructions are to dose 3 times with a week between doses, and to use carbon or do a water change 24 hours after dosing. You'll find different recommendations on whether 3 treatments are necessary, or whether carbon or water changes are necessary, or even if the treatment is necessary. I chose to treat my whole tank and to follow the recommended directions.
QT your shrimp and crabs before treating, as they're unlikely to survive. Again, you'll hear different accounts of shrimp and crab survivability. Corals and clams are unaffected by the medication itself. Corals obviously benefit from removal of wee arthropods that are feasting on them like little coral ticks or fleas.
In the grand scheme of reef pests, redbugs are fairly easy to irradicate.