We used HouseMaster's twice, and both times they missed significant problems. The first house we had an offer in they missed that there was vermiculite in the crawl space. We backed out of that deal due to other problems with the house that we had found ourselves. We found out about the vermiculite later, when another couple that was buying that house also used HouseMaster's to inspect the house and HouseMaster's accidentally e-mailed us their home inspection report. They missed the vermiculite in our inspection, but noticed it in the other couples inspection.
In our current home, HouseMaster's missed that the roof was installed wrong and was leaking. The roof was relatively new, but had been nailed too close to the end of the shingles, which was causing it to leak. During the debriefing of our inspection, we pointed out some water damage on the ceiling and specifically asked if the roof had leaked. The inspector told us that the water damage was most likely from a previous roof that had leaked, but that the current roof was totally fine. That was in June. Skip forward to November when it was raining regularly and our attic was full of water.
HouseMaster's also missed less significant things that has lead us to believe that they were negligent during the inspection. During the winter, we noticed that a couple of our baseboard heaters were not working. We discovered that they weren't wired into the wall. It was an easy fix, but our house is a small rancher and only has 8 baseboard heaters, and they missed that 2 of them weren't working. We have noticed many other things that were also missed during the inspection.
You would expect for a home inspector to miss some minor things during an inspection, but the amount of things that were missed, and the severity of some of the things that were missed was not acceptable.
I would strongly recommend that you do not use HouseMaster's.