That article doesn't confirm, nor deny the effectiveness of Garlic against Marine Ich. It simply says, "there is still much to know".
It may not be the solution, but in my short time as a reefer in the last 8 years, I've used garlic as a alternative to tearing my tank apart to catch fish and Q them. It's worked wonderfully. I've had Ich twice, once in my 55 about 7 years ago, and just recently when our temps started dipping, and I forgot to turn on the extra 2 heaters for our winter months. Ich came, about 2 1/2 weeks of garlic, no fish died, no fish quit eating, nothing. Everything is now back to normal, and the tank is doing wonderfully.
The really odd thing, the 2 clowns I have, were in the 55 and had ich years ago in that breakout, were the only of my fish in my current system, who DIDN'T get ich this time around.
I don't read all the studies, but I've found articles that vary in opinion, and in my experience, it has worked. Garlic will improve your fishs' immune system, and it will help improve the tolerance. It may not cure the ich itself, but it will certainly help your fish fight it off, and make them that much more healthy.