That said, if the block did have an imperfection, we've already established that anyone other than a complete muppet would discover the problem long before it did significant damage to other components in their system and they could get a new (presumably un-flawed) block from Swiftech under their 5-year guarantee.
On that point we disagree. How would you discover it? Take apart the loop? Physically check the block? An airplane that has an issue with corrosion can be physically inspected and I'd bet that the dissimilar metals are used only in areas where such inspection can be easily done. Of course we "can" take apart our loops every 6 months and insure that nothing goes wrong. But are you going to rip apart your rad to discover if the corrosion is landing in there?

What I'm indicating here is that there is a level of impracticality in this scenario. There are a lot of loops out here that don't undergo surgury every 6 months to be certain everything is in good shape. And short of that the effects are out of sight. Are they catastrophic? They might be or they might not be. But there is very little practical way of insuring you aren't the 1 in xxxxx who is about to have a problem. And yes, if the failure occurs around the O-ring area, you could have a serious problem one day when you had no problem the day before.

Again, this isn't meant to be doom and gloom. What I'm indicating is that there are competing parts at the same price and nearly or equally the same performance without this risk. To me the choice is logical and simple. But some may be far happier with a bit more performance and a level of maintenance they've gotten accustomed with.

What I am trying to indicate is there is no way short of checking carefully and regularly to mitigate the risk.

$.02