When you say keep a close eye on the hanger bolts, I'm assuming you mean that they are always snug enough. What, if anything else, should I watch for?
Tight bolts, and keep the header pipe free of rust. It's all you can do.
I get the point on the Ebay pipes, and crappy roads... They always come with a hanger, and a silicone strap but most guys don't get that mounted right, and the pipes weight can/will break off the end of the header pipe.
Careful mounting is important.
I also noticed the 125/150 pipes were listed as one in the Ebay add. I wonder if that infers it is actually the same pipe. RP did not even list the 150 bike at all...
Just guessing but B&L may be on to something with the Bro's pipe... Maybe order one, and verify if it does fit... I would be VERY careful not to mount it tightly until you know it fits... You can return/exchange parts, as long as they are not scratched up from a bad install.