Making piston rings takes skill. Making fine piston rings is an art form.
I have not used any of Bjorn’s rings yet, but I will be. I have an ST G60 Blue Head and about HP .40 that need rings. I’ll be using Bjorn without hesitation. OEM rings work fine, but they often take longer to break in. I like the quicker break-in of Frank/Bjorn’s Meehanite and the narrower ring gap makes for a better seal.
I still have about a dozen of Frank’s rings hanging on my parts wall. I am a hoarder - I ordered spare rings for every ringed engine I owned (at the time) awhile back.
. I’ve only needed to use a few of them so far.