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Not a Metro owner, but I did install the Total Seal rings on a Datsun quite a few years ago. They never gave me any problems, seated up quickly, haven't worn prematurely.
The reason they can decrease friction/increase mileage is that they can function with a lot less spring pressure- the gapless design seals well enough when cold or upon start-up that normal spring pressure isn't needed. Gas pressure takes over, though, so I don't know how much of a FE increase you will get compared to standard rings, at least if you have a long commute where cold starts have a lesser effect. They do have a reputation of maintaining good compression for a long time because of the wear pattern of the two different ring materials.
I think you will need a much more precise step in the standard ring to actually get some gapless benefit. It does need to be a gas seal, after all.
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