I will have to say that I am really impressed with Square Trade, my wife accidentally put her s6 edge through the washing machine. I filled out a claim online around 5:10PM on a Friday, paid a $65.00 deductible and we had a replacement phone on Saturday, the next day, before noon. I know that they usually send you refurbished phones, but if the phone they sent was refurbished, I could not tell it. The experience was way better than any experience that I have had with AT&T or Best Buy on getting a phone replaced.
I have Square Trade on my Note 5 and my son's LG G4 and I will be using them again whenever it comes time for a new phone. Definitely cheaper and faster than AT&T or Best Buy, I don't know about the Samsung Protection Plus.
You usually have 30 days to get insurance on a phone if you don't get it at the time of purchase.