Hi John,
I've just had mine done by Hollygrove of Ringwood. My XF is a 3.0D 2010 with 85k on the clock. It cost about £375 plus labour, using Mahle products (as supplied to Jaguar).
After they'd completed the job we had a look at the magnets which are mounted on the old sump. I didn't have any visible debris or metal filings.
I've since cover 1000 miles and can feel a subtle improvement in gear changes and its quick reactions, especially when cold. It isn't earth shattering but then my Jag only goes on fast A & B roads and not into towns or city's (wife's Golf does all that stuff 😁)
The guidance I've seen is about 10years or 100k, so I would add it to your "to do" list.