Regarding Seasonic reliability... I've been using them for over 10 years, and at least a dozen have been abused around the lab for years, going back to the Super series, the S12s, various non-retail OEM types, the M12s, and the X series. A very few have failed -- all were 300W 80mm fan models I modded with Panaflo 80M fans back in the day when case airflow really was in its infancy. They died after some years use, due most likely to capacitor failure from high internal temperatures. I haven't had any other Seasonics fail. IMO, Seasonics are as good as anything else in the market, most likely better, because their engineering dept is highly conservative & refuse to create products that won't hold up under extreme testing conditions.
(An Aside: Engineering conservatism is one reason why all Seasonics get really loud at maximum load -- their fan controllers have a near exponential curve -- at 400W the fan in an X-650 might not even start, but at full load, it's like 40 dBA! This is because the engineering dept wants the PSUs to be able to run indefinitely at 100% load. The creators of PSUs that keep the fan at low speed even at maximum load are betting that most users will never be able to run their PSUs to full load because they all overbuy power -- ie, a 500W rated PSU will rarely see 250W peak demand in a DIY PC. Not true among server builders, where they like to run PSUs at 60~80% of rated load, which gives highest conversion efficiency, and maximizes the stretch of their hardware $$s. Seasonic was an OEM-only manufacturer for 25 years before they started marketing/selling under their own brand. It still shows.)
I very much trust your experience Mike but the cautious side of me says "Maybe they dropped the ball on this model or have lowered their standards a bit", particularly when I see a buyer who's received two faulty units in a row.
I'm torn as I really need to buy a PSU and get my brother's PC finished but I don't want to rush into buying something I'll regret. Hopefully there'll be some more user reviews soon to help me make a decision.