I am by no means one of those folks that has been doing this for decades. I don't know "old school"... it's all new to me! Well... relatively. Many of these bottled bacteria products have come out only within the last couple years.
Many folks swear by the stuff. They've used it, and it worked for them. But the thing about stuff like this is that you don't know what would've happened if you hadn't used it. And often times folks that swear the stuff works don't have the ammonia/nitrite readings and just assumed it worked because their fish didn't die. Not saying it doesn't work... just saying that it's tough to really prove beyond a doubt that it actually works in all cases, in all tanks. I KNOW a rotting shrimp will work.
The thing I don't like about it though it what does it save you? OK... say it works. You dump the stuff in your tank and you're ready to put a fish in the next day. So you saved yourself a month of cycling time. In the big picture, a month is nothing. Properly stocking a tank takes time, and if you don't have a month to blow in the beginning, that tells me that you're going to be rushing things somewhere else down the road. I'm not a naturally patient person, and this hobby has taught me to "be still" and let the tank try to take care of itself first. The normal saying is true... "nothing good ever happens fast in a reef tank."
Further... if you're using a quarantine tank setup (which we ALL should be), once you get the fish in the QT you still have another month before it goes into the main tank. When I set up my tank, I had my first fish in my QT at the same time my main tank was cycling. My QT was cycling a couple months before I even had water in my main tank. With proper planning, you really don't need "overnight" products.