Jeff Layman wrote:

I've never used drip-line where the piping has holes along its length.
So if that's what you are definitely using, stop reading now!

No, I wasn't sure if that was the only type with fixed 15cm or 30cm
spacing drippers, which would be pretty wasteful considering my tree
spacing.

But I've
used the other type, where you put drip-heads in, a number of times.

In my experience there were slight differences in the diameter of
Gardena and Hozelock tubing (6 and 6.5mm?), and the drip-heads of one
were a slight looser fit in the pipe of the other.

The various ones I'd looked at tried to imply their system required
their parts, but Claber implies compatibility with a lot of the other
names I'd seen

I think I can go with a 1/2" backbone and a tee off per tree to 1/4"
pipe with a couple of adjustable drippers.