I’ve found 4into1 to be quite useless both in the quality of their parts and their customer service.
DSS has a good rep for good parts. I’ve only received good parts from them.
I ordered quite a few ransoms bits (rubber, bolts, cables, electrical, etc..) from vintagecb750.com and they were all of good quality. I had a problem with 1 item and I didn’t know about it until my build was done, 6 months after buying it. I emailed to let them know it failed, didn’t ask for a refund or another, just let them know it failed. They shipped a replacement and I had it in 2 days. Says a lot about them in my mind.
I bought some cheap boots off eBay for my K0 cause that’s all I could find. They were made backwards. Go figure.
750 boots are not all the same. Can’t speak to any other models.