First of all, Istvan guided us through a complete plumbing stack replacement. He helped us work around the house's limitations, and his advice saved us thousands of dollars.
Additionally, Istvan designed and installed our hydronic heated floor system. Again, he proposed pragmatic solutions, did tons of research, and found parts not commonly available here in Canada.
Finally, Istvan did a lot of other smaller jobs around the house, like fixing our water heater by replacing a $25 part rather than having us buy a new one, installing a new softener, helping us choose a filtration system and installing it, and so on.
Istvan's work is impeccable. He's one of the only two contractors we hired so far (out of many) that we didn't have to micromanage to get excellent results. I would highly recommend him for any plumbing projects.