Modem performance and modem selection.

" use a cable tv isolator in front of the modem. this will prevent ground loops between your gear and the cable tv entrance "

you are suggesting the OP get something that he might not even need.

something like this could also cause issues with the return path.

When I mentioned the return path, I was referring to the cable return .
Often pieces will allow signal in but will not let things out and will cause issues that the customer would not be aware of UNLESS he has the proper tools to troubleshoot.   

“ So long as the bandwidth is correct, they are bidirectional. “

Erik, I was a cable tech for 16 yrs and things that I didn’t think would cause issues such as multi plugs that customers would buy ended up being why a trouble call was created.     As I said before, a customer would not know that there is a issue as to them everything is running fine, but when the tech / maintenance shows up at their door they will wonder why.      I have seen this countless times.

another thing that this could cause would be noise on the plant and if there is enough noise on the plant, you can actually slow everyone’s internet down to a crawl or you can create an outage and shut a whole node down.    Again, I have seen this happen and the customer is unaware that they caused this.