I aim for 0.75 and have never had a problem with stuff slipping. Although that’s 3×9 mtb chains.
0.5 sounds like changing it a bit prematurely, but won’t do any harm apart from to your wallet.

There is a chain of thought that says run it till it starts slipping and change everything at once?
Not sure if that works out cheaper in the long run, I’ve changed worn chains in the past and then the new one has started skipping because of worn chainrings.

I thought the whole point of checking the chain was to replace it before it wore the cassette down as its cheaper to replace the chain rather than the whole drive chain?

I’d heard that 1.0mm was probably the trigger point, but some change the chain at 0.75mm to be on the safe side.

The only reason to change the whole drive chain is if the cassette is too worn for the replacement chain to link properly, so is that the case? and if so how have you done that with such low chain wear?

5000km for a cassette should be nowhere near needing replacing on average, if it’s on a reasonably maintained road bike and chains haven’t been used for long beyond .75 wear.

Chain checkers are only a guide, but useful to keep tabs on wear rates. Check when new for a starting point, they’re usually close to .5 then. I replace chains at .75 or soon after so that wheels with different cassettes on always mesh up ok, but one road bike is way beyond 1.0 now and all is running relatively smoothly. Cassette and rings are trashed, but it took a lot of miles to get that far.

It’s a load of old cobblers.
I’ve never had a worn chain slip on worn sprockets or chainrings. Never.

It’s a clever bit of marketing to make people think they are doing essential maintenance like a ‘proper’ cyclist. It’s a great way of making people buy more chains, which in turn means people run newer chains on older cassettes, which in turn makes people buy more cassettes.

But hey, it’s your money.

Exactly this.

My road bike is now 7 years old – original chain and cassette. Not planning on changing them any time soon. Must be upwards of 50,000 miles on them.

I do however appreciate that when I need to change on part i’ll need to change the lot.

It’s a load of old cobblers.
I’ve never had a worn chain slip on worn sprockets or chainrings. Never.
I have several times.
Not good when there’s a pack of charging bullocks chasing you, you put the power down, the chain slips and you’re on your ass. Or when you’re trying pull out of a junction sharpish and the chain slips on the middle ring and again you end up on your ass in the middle of the road.

I don’t change the chain or the rings or the sprockets until things start to malfunction, like above. Then they all get changed, well the big ring and granny last a couple of changes usually.

crikey’s chain never slips as it’s so worn it has become elastic and can form itself to anything vaguely lumpy with ease..

Change if you want to keep the same cassette for a while.

Keep if you intend to run both into the ground.