I was given a Mavic Mini drone as a gift. In the specs it indicates transmission power/video transmission of 4km for the MR1SS5 model. Is this actual fact. Has anyone actually flown theirs that far away from where they are. I have gone about 600m so far, nervous about going further.

And the Mavic Mini 2 says to 10km away? That is a considerable distance.

Also do high voltage transmission lines interfer with transmission control signals at all. We have some high lines adjacent to the ranch.

Let's say ... (almost) everyone has flown 1, 2, 3 or even 5 km, but most of them don't write that ... neither do I ;-). There can of course be interference from transmitter masts, power lines, WLANs and so on, which affect the range, but this is then also displayed in the app.

Hi, One Shot. Thanks for reaching out! Please be advised that the maximum flight range specification is a proxy for radio link strength and resilience, not aircraft battery capability. It only refers to the maximum, one-way flight distance, and the data was measured in an open environment without interference.

Also do high voltage transmission lines interfer with transmission control signals at all.
No

Also do high voltage transmission lines interfer with transmission control signals at all. We have some high lines adjacent to the ranch.

No high voltage transmission lines don't interfer the signal to your MM. But Radio waves, distance, trees, buldings and something else because the MM only have a wireless lan connection.

mini 2 is limited by battery. But dunhill's test in that youtbe vid could have gone a bit further because he was conservative with the outgoing trip battery rationing. So I think it could have gone out for 5km if he really pushed it and the signal would have been very good due to the 10 km transmission range. mini one certainly did 4.6km in his test but the vid feed was getting choppy. In practice I doubt anyone really wanna do complicated flight and film pattern that far.

He was in Hawaii which was pretty clean with radio interference. If you do it in a more urban area the vid becomes bad earlier. You should fly as far as you can see it with your eyes though so really the signal strength is good enough for both models.

I flew yesterday on a river and couldn't get past 1.4km without video freezing. Also at that distance my controller connection started acting up too. Lost control briefly, then I just turned around and flew back. I still had 80% battery at 1.4km (5m30s into flight) and I started the flight with 98%. There was no obstruction between me and the Mini and it's not in an urban area but I was on a river dock.

I My farthest flight with the range extender is about 2300 m, although I think it would be possible to fly a little further.  I have the CE version, the FCC version allows flights twice as long.