Don't blow up and leave you stranded in the middle of nowhere. Yes, I'm aware of a couple dying, but very, very, very, very, very rare.
Realistically...... no advantage If you currently have a fully functional s1 ptu and you replace it with a s2 ptu you will gain NOTHING Will the s1 ptu last forever ? No, but neither will the s2 ptu..... or the starter motor, alternator, fuel pump etc Electrical components all fail sooner or later I am currently using both ptu's and have NEVER had a failure (but I carry spares of each, just in case)
S1 PTU's have a proven failure record. Keep a spare or change to S2. Too many people have been left on the side of the road because of them. The PTU was a recalled item in the US. That's proof enough for me...
I swapped my S1 for an S2 before a big road trip to the middle of nowhere, otherwise I'd have stuck with the S1 and just swapped if/when it died.