Hydrofarms can work. Yes. I use one on my QT rack. It's in temporary use at the most.
It's not as accurate or steady as my Herpstat though. Kitedemon(who no longer posts), was notorious for hating Hydrofarms. He went through testing dozens and concluded that they can have huge temp swings and/or just fail to properly function. In the end, Hydrofarms are designed for hydroponic gardening, not reptile enclosures. It was just merely adopted into reptile keeping, while the Herpstat was designed specifically for it.
I think the Hydrofarm works way better than the Zoomed/Zilla/Petstore T-stats. But I still prefer the Herpstat. It doesn't matter how many snakes you have or what kind of enclosures you use. It's all about how much are you willing to pay for the safety of your animal and the accuracy of your temperature regulation. I'm not saying, don't use a Hydrofarm. Tons of people have used it fine. But if you're willing to dish out the money, buy something that is guaranteed to be quality and reliable.
And holy crap @ the heat rocks.....Most dangerous thing you can put into a reptile enclosure. I can guarantee that no body in the reptile hobby will ever recommend using one. And anyone using a heat rock, shouldn't own a reptile......