Robin wrote:
I'd welcome views from anyone who has used one or other or - even
better - both of the "lightweight" concrete and the uPVC slotted
posts. I'm particularly interested in strength and (so far as
possible given they are new-ish) durability.

The job is a fence for a small garden in a sheltered (city) position.
At least 5 foot panels; and on a slight slope so at least 6 inch
gravel. I have ruled out traditional concrete slotted posts: I am
too old/weak for even the 8 foot ones let alone the 9 foot I'd
prefer. So I'm tempted by either the 8'9" Supreme Concrete Lite
posts or the 9' Supalite uPVC posts. But I've been unable to see
either of them or find independent views. Travis Perkins list the
Supreme Concrete but there are none in stock near me and no info on
www.supremeconcrete.co.uk. There are no Supalite stockists near me
and I've not been able to find any in use. While the posts sound a
good idea (with a metal core to the larger ones) I'm more dubious
about how they and the matching gravel boards would stand up to
general wear and tear.

The more metal they have, the sooner they fall apart, especially if the
concrete is 'lite' - the metal rusts, expands and the concrete falls off in
chunks.
For what you'd pay for these things you could probably get a fencing
contractor to do the job for you with proper concrete posts...also you're
way off with your measurements - you don't need 9 ft posts for a 5 foot
fence, you need six foot six ones.

PVC is generally crap WRT fencing, it suffers in direct sunlight and becomes
brittle.