It does not cover anything deemed consumable, e.g. brakes, shock abosorbers, clutch. I was told also the suspension components, so I expect the bushes are also excluded.
From another member, I understand electrical faults are also excluded.
However, I believe it should cover the major mechanical parts, such as gearbox, engine and driveshafts.
I have not read the small print, but I will in about 6 months time,
Whether it is worth it, depends. It you never claim, then no. Obviously it is priced so that they do not lose money, so obviously Porsche believe not that many cars are going to fail.
However, if the main items do fail, then the bill is going to be in 4 or 5 figures.
A new engine will cost 8-15K depending on whether you have a C2 or GT2 (or something like that) and a new gearbox 5K+. Whilst OPCs seem reluctant to rebuild things, preferring to put in a new engine or gearbox instead of replacing a few bearings and flushing the oil ways, independents can rebuild things considerably more cheaply, although you are looking at thousands.
The problem with independents (or even doing it yourself) is that the warranty and extended warranty is voided.
Clearly, all you need is one major issue before the car hits 10 years or 120K miles, and you are laughing. Bear in mind that the OPCs charge about £100 per hour, so any major work is expensive. You can also practice servicing tourism, and get major work done at a French or other OPC (where labour rates are lower).
I would say it is worth it, but you could also put £725 in a savings account every year instead. Over the long term you should be even or slightly better off, unless you are unlucky.
So ask yourself one question, do you feel lucky?